BACTERIA 29 



those who drink the water, there are no longer typhoid bacilli in the 

 water. The bacteriologic examination of drinking-water after an 

 epidemic has developed, is in the large majority of instances, a useless 

 procedure. A city's water-supply should be examined daily in order 

 to be of value. The weapons used in this warfare among bacteria 

 are many and varied. Some simply eat up the food supply and the 

 invaders die of starvation. Others produce waste products which are 

 harmful to other species. Anthrax bacilli planted in sterile cholera 

 cultures are greatly weakened. Sterile cultures of the pyocyaneus 

 dissolve anthrax bacilli. Some change the reaction of the common 

 medium by the development of acid or alkali and their enemies die. 

 The streptococcus kills the plague bacillus, and thus the conflict of 

 nations and races goes on among the unicellular organisms much as 

 it does among the lords of creation. 



Symbiosis. Some species form allied armies and contend against 

 a common enemy or overrun a foreign country. The pus bacteria are 

 found in many combinations and most men die from diseases in 

 which these cocci play an important part. After the tubercle bacillus 

 has fed on one's lungs for years and prepared the soil, some pus 

 germ finds its way in before death and contributes largely to its com- 

 ing. The cancer cell opens up ports of entry through which pus 

 organisms enter. The lesions of syphilis are plundered and looted by 

 the hordes of cocci. Thus, as Mayo has pointed out, sepsis plays an 

 important role in the last acts of the three great tragedies of life; 

 tuberculosis, cancer and syphilis. Some pathogenic bacteria receive 

 aid from organisms which by themselves are harmless. The tetanus 

 bacillus is much more virulent when it enters the animal body in 

 company with certain saprophytes. When alone, the phagocytes 

 speedily fall on and devour it, while certain products of the growth 

 of its friend repel the phagocytes. 



Capsules. Some bacteria are surrounded by mucilaginous capsules. 

 When two or more individuals are attached, the capsule usually 

 includes the group, and when many are imbedded in one large capsule 

 the whole is known as a zooglia. The capsule is believed to be formed 

 for protective purposes, since many bacteria develop them only when 

 in the animal or when grown in animal fluids, secretions or excre- 



