THE PHENOMENA OF INFECTION 437 



not necessarily possess a form recognizable to our limited 

 sense even when aided by the most perfect lenses. 



One of the most important results of our work, in our 

 opinion, is the demonstration that bacteria are chemically 

 not simple, but quite complicated in structure. Morpho- 

 logically, they show but little or no differentiation in struc- 

 ture, but chemically they are quite as complicated and 

 complex as many of the cells of the higher animals. They 

 contain carbohydrates, nuclein bodies, and polymers of the 

 mono- and diamino-acids. They are glyconucleoproteins. 

 We interpret this as signifying that functionally they are 

 highly developed. 



While an infecting virus may be solid, semisolid, gela- 

 tinous, or liquid, we will, in the further consideration of 

 the phenomena of infection, take the particulate type, the 

 bacterium, as an example of an infecting agent. 



What are some of the capabilities of a bacterial cell? In 

 the first place it possesses that attribute which distinguishes 

 and characterizes all living matter the capability of growth 

 and reproduction. In order to grow and multiply its 

 molecular structure must be labile in a sate of constant 

 change. Some bacteria under certain conditions may pass 

 into a resting state characterized by the formation of spores, 

 but these are awakened into life when the environment 

 becomes fit, and the spore develops into the active form 

 when it infects. In all instances the active, infecting agent 

 is a living protein, capable of growth and multiplication. 

 In order to do this it must carry on a constant exchange 

 in matter with the medium in which it exists. It must 

 assimilate and eliminate. It must absorb groups from the 

 molecules about it, and cast out those which it has already 

 used. Stop this process and the continuation of life is 

 impossible. Every living cell, be it bacterial, vegetable, 

 or animal, must feed or cease to exist. Besides, a cell is 

 limited in its food supply by that which lies within its 

 reach. There must, therefore, be a certain supporting 

 relation between the bacterial cell and the medium. The 

 groups derived from the medium must fit into the molecular 



