The following directions for fumigating with hydrocyanic acid gas are taken from Professor Herrick's circular published by the Cornell Reading Course:

Hydrocyanic acid gas has been used successfully against household insects and will probably be used more and more in the future. It is particularly effective against bed-bugs, and cockroaches, but because it is such a deadly poison it must be used very carefully.

The gas is generated from the salt potassium cyanid, by treating it with sulfuric acid diluted with water. Potassium cyanid is a most poisonous substance and the gas emanating from it is also deadly to most, if not all, forms of animal life. The greatest care must always be exercised in fumigating houses or rooms in buildings that are occupied. Before fumigation a house should be vacated. It is not necessary to move furniture or belongings except brass or nickel objects, which may be somewhat tarnished, and butter, milk, and other larder supplies that are likely to absorb gas. If the nickel and brass fixtures or objects are carefully covered with blankets they will usually be sufficiently protected.

There may be danger in fumigating one house in a solid row of houses if there is a crack in the walls through which the gas may find its way. It also follows that the fumigation of one room in a house may endanger the occupants of an adjoining room if the walls between the two rooms are not perfectly tight. It is necessary to keep all these points in mind and to do the work deliberately and thoughtfully. The writer has fumigated a large college dormitory of 253 rooms, once a year for several years, without the slightest accident of any kind. In order to fumigate this building about 340 pounds of cyanid and the same amount of sulfuric acid were used each time. In addition to this, the writer has fumigated single rooms and smaller houses with the gas. In one instance the generating jars were too small; the liquid boiled over and injured the floors and the rugs. Such an accident should be avoided by the use of large jars and by placing old rugs or a quantity of newspapers beneath the jars.

The Proportions of Ingredients

Experiments and experience have shown that the potassium cyanid should be ninety-eight per cent pure in order to give satisfactory results. The purchaser should insist on the cyanid being of at least that purity, and it should be procurable at not more than forty cents per pound. The crude form of sulfuric acid may be used. It is a thickish, brown liquid and should not cost more than four or five cents a pound. If a room is made tight, one ounce of cyanid for every one hundred cubic feet of space has been shown to be sufficient. It is combined with the acid and water in the following proportions:

Suppose a room to be 12 by 15 by 8 feet. It will contain 12 × 15 × 8, or 1440 cubic feet. For convenience the writer always works on the basis of complete hundreds; in this case he would work on the basis of 1500 cubic feet, and thus be sure to have enough. The foregoing room, then, would require 15 ounces of cyanid, 15 ounces of sulfuric acid, and 45 ounces of water. The room should be made as tight as possible by stopping all the larger openings, such as fireplaces and chimney flues, with old rags or blankets. Cracks about windows or in other places should be sealed with narrow strips of newspaper well soaked in water. Strips of newspaper two or three inches wide that have been thoroughly soaked in water may be applied quickly and effectively over the cracks around the window sash and elsewhere. Such strips will stick closely for several hours and may be easily removed at the conclusion of the work.

While the room is being made tight, the ingredients should be measured according to the formula already given. The water should be measured and poured first into a stone jar for holding at least two gallons. The jar should be placed in the middle of the room, with an old rug or several newspapers under it in order to protect the floor.

The required amount of sulfuric acid should then be poured rather slowly into the water. This process must never be reversed; that is, the acid must never be poured into the jar first. The cyanid should be weighed and put into a paper bag beside the jar. All hats, coats, or other articles that will be needed before the work is over should be removed from the room. When everything is ready the operator should drop the bag of cyanid gently into the jar, holding his breath, and should walk quickly out of the room. The steam-like gas does not rise immediately under these conditions, and ample time is given for the operator to walk out and shut the door. If preferred, however, the paper bag may be suspended by a string passing through a screw eye in the ceiling and then through the keyhole of the door. In this case the bag may be lowered from the outside after the operator has left the room and closed the door.

The writer has most often started the fumigation toward evening and left it going all night, opening the doors in the morning. The work can be done, however, at any time during the day and should extend over a period of five or six hours at least. It is said that better results will be obtained in a temperature of 70° F., or above, than at a lower degree.

At the close of the operation the windows and doors may be opened from the outside. In the course of two or three hours the gas should be dissipated enough to allow a person to enter the room without danger. The odor of the gas is like that of peach kernels and is easily recognized. The room should not be occupied until the odor has disappeared.

Fumigating a Large House

The fumigation of a large house is merely a repetition, in each room and hall, of the operations already described for a single room. All the rooms should be made tight, and the proper quantities of water and sulfuric acid should be measured and poured into jars placed in each room with the cyanid in bags besides the jars. When all is ready, the operator should go to the top floor and work downward because the gas is lighter than air and tends to rise.

Precautions

The cyanid should be broken up into small pieces not larger than small eggs. This can best be done on a cement or brick pavement. It would be advantageous to wear gloves in order to protect the hands, although the writer has broken many pounds of cyanid without any protection on the hands. Wash the hands thoroughly at frequent intervals in order to remove the cyanid.

The operations of the work must be carried out according to directions.

The work should be done by a calm, thoughtful and careful person—best by one who has had some experience.

Conspicuous notices of what has been done should be placed on the doors, and the doors should be locked so that no one can stray into the rooms.

The gas is lighter than air, therefore one should always begin in the rooms at the top of the house and work down.

After fumigation is over the contents of the jar should be emptied into the sewer or some other safe place. The jars should be washed thoroughly before they are used again.

It must be remembered that cyanid is a deadly poison; but it is very efficient against household insects, if carefully used, and is not particularly dangerous when properly handled.

LESIONS PRODUCED BY THE BITE OF THE BLACK-FLY

While this text was in press there came to hand an important paper presenting a phase of the subject of black fly injury so different from others heretofore given that we deem it expedient to reproduce here the author's summary. The paper was published in The Journal of Cutaneous Diseases, for November and December, 1914, under the title of "A Clinical, Pathological and Experimental Study of the Lesions Produced by the Bite of the Black Fly (Simulium venustum)," by Dr. John Hinchman Stokes, of the University of Michigan.

Resume and Discussion of Experimental Findings

The principal positive result of the work has been the experimental reproduction of the lesion produced by the black-fly in characteristic histological detail by the use of preserved flies. The experimental lesions not only reproduced the pathological pictures, but followed a clinical course, which in local symptomatology especially, tallied closely with that of the bite. This the writer interprets as satisfactory evidence that the lesion is not produced by any living infective agent. The experiments performed do not identify the nature of the toxic agent. Tentatively they seem to bring out, however, the following characteristics.

1. The product of alcoholic extraction of flies do not contain the toxic agent.

2. The toxic agent is not inactivated by alcohol.

3. The toxic agent is not destroyed by drying fixed flies.

4. The toxic agent is not affected by glycerin, but is, if anything, more active in pastes made from the ground fly and glycerin, than in the ground flies as such.

5. The toxic agent is rendered inactive or destroyed by hydrochloric acid in a concentration of 0.25%.

6. The toxic agent is most abundant in the region of the anatomical structures connected with the biting and salivary apparatus (head and thorax).

7. The toxic agent is not affected by a 0.5% solution of sodium bicarbonate.

8. The toxic agent is not affected by exposure to dry heat at 100° C. for two hours.

9. The toxic agent is destroyed or rendered inactive in alkaline solution by a typical hydrolytic ferment, pancreatin.

10. Incomplete experimental evidence suggests that the activity of the toxic agent may be heightened by a possible lytic action of the blood serum of a sensitive individual, and that the sensitive serum itself may contain the toxic agent in solution.

These results, as far as they go (omitting No. 10), accord with Langer's except on the point of alcoholic solubility and the effect of acids. The actual nature of the toxic agent in the black-fly is left a matter of speculation.

The following working theories have suggested themselves to the writer. First, the toxin may be, as Langer believes in the case of the bee, an alkaloidal base, toxic as such, and neutralized after injection by antibodies produced for the occasion by the body. In such a case the view that a partial local fixation of the toxin occurs, which prevents its immediate diffusion, is acceptable. Through chemotactic action, special cells capable of breaking up the toxin into harmless elements are attracted to the scene. Their function may be, on the other hand, to neutralize directly, not by lysis. This would explain the rÔle of the eosinophiles in the black-fly lesion. If their activities be essential to the destruction or neutralization of the toxin, one would expect them to be most numerous where there was least reaction. This would be at the site of a bite in an immune individual. A point of special interest for further investigation, would be the study of such a lesion.

Second, it is conceivable that the injected saliva of the fly does not contain an agent toxic as such. It is possible, that like many foreign proteins, it only becomes toxic when broken down. The completeness and rapidity of the breaking down depends on the number of eosinophiles present. In such a case immunity should again be marked by intense eosinophilia.

Third, lytic agents in the blood serum may play the chief rÔle in the liberation of the toxic agent from its non-toxic combination. An immune individual would then be one whose immunity was not the positive one of antibody formation, but the negative immunity of failure to metabolize. An immune lesion in such a case might be conceived as presenting no eosinophilia, since no toxin is liberated. If the liberation of the toxin is dependent upon lytic agents present in the serum rather than in any cellular elements, a rational explanation would be available for the apparent results (subject to confirmation) of the experiment with sensitive and immune sera. In this experiment it will be recalled that the sensitive serum seemed to bring out the toxicity of the ground flies, and the serum itself seemed even to contain some of the dissolved or liberated toxin. The slowness with which a lesion develops in the case of the black-fly bite supports the view of the initial lack of toxicity of the injected material. The entire absence of early subjective symptoms, such as pain, burning, etc., is further evidence for this view. It would appear as if no reaction occurred until lysis of an originally non-toxic substance had begun. Regarding the toxin itself as the chemotactic agent which attracts eosinophiles, its liberation in the lytic process and diffusion through the blood stream attracts the cells in question to the point at which it is being liberated. Arriving upon the scene, these cells assist in its neutralization.

The last view presented is the one to which the author inclines as the one which most adequately explains the phenomena.

A fourth view is that the initial injection of a foreign protein by the fly (i.e., with the first bite) sensitizes the body to that protein. Its subsequent injection at any point in the skin gives rise to a local expression of systematic sensitization. Such local sensitization reactions have been described by Arthus and Breton, by Hamburger and Pollack and by Cowie. The description of such a lesion given by the first named authors, in the rabbit, however, does not suggest, histopathologically at least, a strong resemblance to that of the black-fly. Such an explanation of many insect urticariÆ deserves further investigation, however, and may align them under cutaneous expressions of anaphylaxis to a foreign protein injected by the insect. Depending on the chemical nature of the protein injected, a specific chemotactic reaction like eosinophilia may or may not occur. Viewed in this light the development of immunity to insect bites assumes a place in the larger problem of anaphylaxis.

Summary

In order to bring the results of the foregoing studies together, the author appends the following rÉsumÉ of the clinical data presented in the first paper.

The black-fly, Simulium venustum, inflicts a painless bite, with ecchymosis and hÆmorrhage at the site of puncture. A papulo-vesicular lesion upon an urticarial base slowly develops, the full course of the lesion occupying several days to several weeks. Marked differences in individual reaction occur, but the typical course involves four stages. These are, in chronological order, the papular stage, the vesicular or pseudovesicular, the mature vesico-papular or weeping papular stage and the stage of involution terminating in a scar. The papule develops in from 3 to 24 hours. The early pseudovesicle develops in 24 to 48 hours. The mature vesico-papular lesion develops by the third to fifth day and may last from a few days to three weeks. Involution is marked by cessation of oozing, subsidence of the papule and scar-like changes at the site of the lesion. The symptoms accompanying this cycle consist of severe localized or diffused pruritus, with some heat and burning in the earlier stages if the oedema is marked. The pruritus appears with the pseudovesicular stage and exhibits extraordinary persistence and a marked tendency to periodic spontaneous exacerbation. The flies tend to group their bites and confluence of the developing lesions in such cases may result in extensive oedema with the formation of oozing and crusted plaques. A special tendency on the part of the flies to attack the skin about the cheeks, eyes and the neck along the hair line and behind the ears, is noted. In these sites inflammation and oedema may be extreme.

A distinctive satellite adenopathy of the cervical glands develops in the majority of susceptible persons within 48 hours after being bitten in the typical sites. This adenopathy is marked, discrete and painful, the glands often exquisitely tender on pressure. It subsides without suppuration.

Immunity may be developed to all except the earliest manifestations, by repeated exposures. Such an immunity in natives of an infested locality is usually highly developed. There are also apparently seasonal variations in the virulence of the fly and variations in the reaction of the same individual to different bites.

Constitutional effects were not observed but have been reported.