CONTAGIOUS DISEASES. 265 



and I hope that I have not tried the patience of the audience 

 too much in considering matters that perhaps may seem 

 unconnected with the subject before us. But, as I have 

 already said, everyone acts so much more intelligently when 

 the}' understand why they are doing a thing, I have 

 thought it best to risk the trying of your patience with the 

 matters that have so far eniragcd our attention, the bearina: 

 of which I am sure you will see later. There are many 

 different forms of this minute vegetable life, the bacteria, 

 notwithstanding they are so very small and simple in struc- 

 ture ; they grow, many of them, under different circumstances 

 and conditions ; they differ in size and shape, so that by 

 studying their different life histories the expert is readily 

 able to recognize and classify them. Xow, it is the gi'owth 

 of some of these germs, the bacteria, in some part of the 

 human body that produces the contagious diseases ; one kind 

 of germs fixing themselves in the throat or nostrils and by 

 their development producing diphtheria, another kind find- 

 ing their way into the intestinal canal and by their gi'owth 

 producing typhoid fever, another scarlet fever, another 

 cholera, etc. 



That these bacteria are the real factors in the causino^ of 

 contagious disease is believed by nearly all who are familiar 

 with the teachings of sanitary science. As has already i)een 

 said, this conclusion has not been drawn from theorj^ and 

 guesswork, but it has been the result of careful, patient 

 work and study in the chemical laboratory and the workshop 

 of the microscopist. These careful and exact observations 

 and experiments have been carried on, not by a single ob- 

 server, but by investigators in all countries, and all have 

 arrived at the same general conclusion. In fact, the trutli 

 that these bacteria, developing in' some part of the human 

 body, produce disease has been proven over and over again 

 by exact and painstaking experiments. 



Many of these experiments are ingenious and interesting, 

 but we have only time to briefly allude to some of them, 

 and to show on the screen some of the different forms of 

 bacteria that are believed to cause by their growth in some 

 part of the human body the different forms of contagious 

 diseases, as we must pass on to the important part of our 



