COLLOIDS AND LIFE 61 



(c) Specificity; Absolute specificity. 



{d) Selective adsorption; Staining. 



{e) Peculiarities of filtra- The same. 



tion; 



(/) Some can be evapo- The same is true for bac- 



rated to dryness and teria.^ 



then readily redis- 



solved in water; 



{g) Easily coagulated; "Probably coagulation 



kills them in sunlight." 



The general opinion is as stated by Dr. Rohland : 

 "Bacteria are themselves of a colloidal nature." 



At the other end of the scale of life one may not 

 ignore facts such as that the human in the third 

 month of intra-uterine existence is a system that 

 consists of ninety -four per cent of water. But here 

 it is evident that to describe the organism as a col- 

 loid system does not solve the difficulties of the or- 

 ganism, even considered merely from the point of 

 view of colloid chemistry; since, for example, to say 

 that the brain is colloidal, so far from solving the prob- 

 lem of the brain, at once raises the question why it 

 is that, though normally the human brain begins to 

 shrink at man's early maturity, his psychic powers 

 continue to increase for many years. 



^ 5eeCharlesV.Chapin, "The Air as a Vehicle of Infection." Harvey Lecture, 

 1913. 



