524 PROTOZOA 



Our best results on corneas have been obtained with the following 

 technique : Fix in Zenker's fluid for from four to eight hours ; wash in 

 running water over night; place in 95 per cent, alcohol (changing in 

 two hours to fresh) for twenty-four hours, then in absolute alcohol for 

 twenty-four hours. Imbed in paraffin. The cuts should be from 3/> to 

 5, thick. Stain with (1) eosin and methylene blue eosin half an hour, 

 methylene blue two minutes; (2) Heidenhain's iron hsematoxylin ; (3) 

 Bovrel, modified by Calkins. 



Susceptibility of Different Animals. Horses, rabbits, sheep, monkeys, 

 and guinea-pigs are susceptible. The pulp and serum obtained from 

 an epidemic of cowpox took feebly in calves in a moderate percentage 

 of those inoculated. The characteristic vaccine bodies were found 

 practically identical with those in vaccinia, except that the bodies were 

 a little larger and more irregular in outline. 



The Preparation of Vaccine. For the following suggestions I am 

 indebted to Dr. J. H. Huddleston, who has had the immediate charge 

 of the production of vaccine for the New York Health Department 

 for some years: 



SEED VIRUS. A sufficient amount of vaccine virus should be on 

 hand to vaccinate forty to fifty persons. Five children in good health, 

 and not previously vaccinated, should then be vaccinated each in a spot 

 the size of a ten-cent piece. On the fifth day after vaccination the top 

 of the resulting vesicle should be removed and sterilized bone slips be 

 rubbed on the base thus exposed. It should be possible in this manner 

 to charge at least from one to two hundred slips on each side of the slip 

 from each child. The slips should be allowed a moment in which to 

 dry and then placed in a sterilized box, in which, if kept in cold storage, 

 they will probably remain efficient for at least two or three weeks. 



ANIMALS. The preferable animals are female calves, from two to 

 four months of age, in good condition and free from any skin disease. 

 These can easily be vaccinated on the posterior abdomen and inside 

 of the thighs by placing them on an appropriate table. It is possible 

 that on account of the character of the available supply older animals 

 may be desirable, but the calves take more typically and are more 

 easily handled. When an animal is too old to be thrown and held 

 without difficulty it may be vaccinated on the rump, each side of the 

 spine; but the skin there is tougher than on the posterior abdomen 

 and inside of the thighs, and the resulting virus, though efficient, is 

 not so easily emulsified. 



VACCINATION. The calf should be cleaned thoroughly, including 

 the feet and the tail, and the hair should be clipped from the end of the 

 tail. Next, the posterior abdomen and insides of the thighs are shaved 

 and the skin beneath washed in succession with soap and water, ster- 

 ilized water and alcohol, and then dried with a sterile towel. On this 

 area there are now made about one hundred scarifications, each from 

 one-quarter to one-half of an inch square. The scarification is made 

 most easily by cross-hatching with a six-bladed instrument, the blades 

 being about one-thirtieth of an inch apart. The scarification is super- 



