7 6z THE POPULAR SCIENCE MONTHLY, 



knackers and butchers who break and handle the bones of animals 

 which have died of anthrax. 



The period of incubation is very short. An ox which has been at 

 work may return to the stall apparently healthy. He eats as usual ; 

 then lies down on his side and breathes heavily, while the eyes are still 

 clear. Suddenly his head drops, his body grows cold ; at the end of 

 an hour the eye becomes glazed ; the animal struggles to get up, and 

 falls dead. In this case, the illness has only lasted for an hour and a 

 half (Empis). 



In order to prove that the disease is really caused by Bacillus an- 

 thracis, Pasteur inserted a very small drop of blood, taken from an 

 animal which had recently died of anthrax, in a glass flask which con- 

 tained an infusion of yeast, neutralized by potassium and previously 

 sterilized. In twenty-four hours the liquid, which had been clear, was 

 seen to be full of very light flakes, produced by masses of bacilli, readily 

 discernible under the microscope. A drop from the first flask produced 

 the same effect in a second, and from that to a third, and so on. By 

 this means the organism was completely freed from all which was for- 

 eign to it in the original blood, since it is calculated that, after from 

 eight to ten of such processes, the drop of blood was diluted in a vol- 

 ume of liquid greater than the volume of the earth. Yet the tenth, 

 twentieth, and even the fiftieth infusion would, when a drop was in- 

 serted under the skin of a sheep, procure its death by splenic fever, 

 with the same symptoms as those produced by the original drop of 

 blood. The bacillus is, therefore, the sole cause of the disease. 



These cultures have often since been repeated by numerous observ- 

 ers, so that the microbe has been studied in all its forms, and the ex- 

 tent of its polymorphism has been ascertained. At the end of two 

 days the bacterium, which, while still in the blood, is of a short abrupt 

 form, displays excessively long filaments, which are sometimes rolled 

 up like a coil of string. In about a week many of the filaments con- 

 tain refracting, somewhat elongated nuclei. These nuclei presently 

 form chaplets, in consequence of the rupture of the cell-wall of the rod 

 which gave birth to them ; others, again, float in the liquid in the form 

 of isolated globules. These nuclei are the spores or germs of the mi- 

 crobes, which germinate when placed in the infusion, become elongated, 

 and reproduce fresh bacilli. 



These spores are much more tenacious of life than the microbes 

 themselves. The latter perish in a temperature of 60, by desiccation, 

 in a vacuum, in carbonic acid, alcohol, and compressed oxygen. The 

 spores, on the other hand, resist desiccation, so that they can float in the 

 air in the form of dust. They also resist a temperature of from 90 to 

 95, and the effects of a vacuum, of carbonic acid, of alcohol, and com- 

 pressed oxygen. 



In 1873 Pasteur, aided by Chamberland and Roux, carried on some 

 experiments on a farm near Chartres, in order to discover why this dis- 



