74 THE GERM THEORY OF DISEASE. 



the disease. If, however, this weakened bacillus be allowed 

 to form spores, these spores will produce the virulent type of 

 the disease. If this observation be confirmed by further re- 

 search, it will become an important element in sanitary and 

 prophylactic measures, especially so if it be found true of any 

 considerable number of disease germs. 



It will be seen at once that the thought contained here has 

 an important bearing upon the propagation of yellow fever, 

 cholera and typhoid fever. If we suppose that the power of 

 forming spores only comes with more or less gradual drying 

 of the voided organisms, and that these organisms are not 

 eliminated by the lungs and sweat glands but only with the 

 excreta, therefore, not liable to be transplanted by immediate 

 passage through the air, we are at once able to understand 

 the clinical facts observed as to communicability of these 

 diseases. 



SUMMING UP. 



Having passed in review, briefly, the rise and progress of 

 the Germ Theory of Disease, we may sum up the principal 

 points thus : 



1st. In the seventeenth and eighteenth centuries, intelligent 

 observers of contagious diseases, after much study of the sub- 

 ject, came to the conclusion they were caused and propagated 

 by a process identical with or similar to fermentation and 

 decomposition. 



2d. There was much study of the processes of fermentation 

 and decomposition, in order to arrive at a more clear under- 

 standing of the causes of epidemic and contagious diseases 

 with the view of prevention and cure. These experiments 

 demonstrated that the fermentations and decompositions were 

 something different from ordinary chemical phenomena. 



3d. The yeast plant was discovered by Schwan and Latour, 

 in 1838. These gentlemen announced distinctly that the 



