ETIOLOGY— CAUSES OF DISEASE 225 



and also in many vegetable and animal substances. In 1683 the discoveries 

 were illustrated by means of wood-cuts, and Professor Crookshank, from 

 whose historical account in his work on Bacteriology these facts are quoted, 

 remarks that there can be little doubt that the drawings were intended to 

 represent leptothrix filaments, vibrios, and spirilla. In another communi- 

 cation in 1692 Kircher gives some idea of the size of these small organisms 

 by stating that they were a thousand times smaller than a grain of sand. 

 Further observations were made by Nicolas Andre in 1701, Lancisi in 1710, 

 and in 1721 the plague in Toulon and Marseilles was attributed to the 

 presence of animalcules, and the theory began to be entertained, amidst 

 considerable ridicule, that all diseases arose from vermicules. Scientific 

 knowledge of the subject was considerably advanced by the writings of 

 Midler, who criticised the previous researches, which, he contended, had been 

 too much directed to the finding of new organisms. Midler devoted him- 

 self to a consideration of the forms, movements, and other biological char- 

 acters of the microbes, and attempted a system of classification. At this 

 time the question of the origin of micro-organisms became paramount, and 

 the theory of spontaneous generation with its alternative, development from 

 pre-existing germs, was widely discussed. Many supporters were found for 

 the theory of spontaneous generation, but the balance of the evidence, 

 obtained by numerous experiments, was in favour of the germ theory. 

 Even as late as 1872 Bastian published an account of his experiments with 

 the object of proving that spontaneous generation actually took place. He 

 found that decoctions of turnip and cheese, which had been filtered and 

 boiled for ten minutes and hermetically sealed during the boiling, con- 

 tained micro-organisms after a time. This evidence was very soon met 

 by the further discovery that in milk, infusions of hay, and other sub- 

 stances the spores of bacilli are present, and that they are not destroyed 

 by boiling. Tyndall further demonstrated that if the method on which 

 Bastian relied was repeated two or three times, all the spores of organisms 

 were destroyed ; and thus the last attempt to demonstrate the truth of the 

 theory of spontaneous generation utterly and entirely failed. During the 

 controversy on the subject of spontaneous generation, several investigators, 

 Latour, Schwann, Bassi. Henley, Davaine, Pasteur, and others, were work- 

 ing steadily in reference to the functions of bacteria, the various processes 

 of fermentation, and production of disease. In 1850 Davaine and Rayer 

 discovered a rod-like body in the blood of a sheep that had died of splenic 

 fever (anthrax); Pollender also discovered similar bodies in the same disease, 

 in the blood of cattle. There is no doubt that this rod-like body was the 

 organism which is now familiarly known as the bacillus anthracis. It was 

 not, however, until further investigations had been carried on by Davaine, 



