ZOOLOGY, ENTOMOLOGY, AND MEDICINE 237 



taking from an animal infected with variola some blood and 

 injecting it into another animal of the same species, he found 

 that it produced a diseased condition similar to that of the first 

 animal, but in a less virulent form, and that it soon subsided, 

 and that it further protected that animal from subsequent at- 

 tacks. 



On May 4th, 1796, Dr. Jenner injected into the arm of a 

 boy a small quantity of lymph, obtained from a milk maid 

 affected with variola, and found that this produced results sim- 

 ilar to those obtained in his animal experiments; the disease 

 was less virulent and the subject soon was protected from it. 

 This was the first injection into man of a substance to protect 

 him against the ravages of disease. Later in the same year he 

 used the lymph of cows and called this liquid vaccine. With this 

 liquid he protected the lives of thousands from the ravages of 

 smallpox. 



Van Helmont and Needham, after a number of years of 

 study of these small organisms offered to the world the theory 

 that these forms of life arose by spontaneous generation in 

 such fluids as meat infusions and other organic solutions even 

 after they had been boiled. This was contested by Spallanzani, 

 who showed that when a meat infusion had been boiled three 

 quarters of an hour and kept from contact with the air, the de- 

 velopments of micro organisms would not take place. It was 

 then claimed by the adherents of the theory of spontaneous 

 generation that the expulsion of air by boiling and the arrange- 

 ments which prevented it frorn re-entering the vessels also pre- 

 vented spontaneous generation. Schulze and Schwan then de- 

 vised methods to permit the entrance of air after it had been 

 heated in a glass tube or passed through sulphuric acid. Schwan 

 also showed that certain poisonous chemicals when added to 

 meat infusions prevented the development of micro organisms, 

 and these chemicals we now call antiseptics. Schroeder al- 

 lowed air to enter vessels containing boiled organic matters, 

 through glass tubes, which had been plugged with cotton; no 

 growth of organisms resulted. This is the method now used 

 to keep pure cultures of bacteria from becoming contaminated. 



Pasteur in 1860 showed that a short boiling of an infusion 

 of organic matter was not sufficient to kill all micro organisms 

 and that some could withstand the temperature of boiling water 



