PROPERTIES OF THE BACTERIOPHAGE 281 



ments I have obtained comparable results. However, it is only fair to 

 state that those who have questioned the correctness of my findings 

 have generally performed their experiments under conditions differing 

 from mine, using slower speeds for the centrifugation.* It is evident 

 that an enrichment of the lower layers may be obtained, although it is 

 never possible to render the upper layers entirely free of corpuscles. 

 Levaditi and Nicolau''^^ ^^ve shown that the same thing happens with 

 the ultraviruses of rabies and of vaccinia. As a matter of common 

 experience, it is well known that it is extremely difficult to obtain a 

 sterile supernatant fluid by centrifugation of a bacterial suspension. 

 There is all the more reason to encounter this same difficulty with 

 ultraviruses. 



Nature of the '^substance" of the bacteriophage corpuscle 



We know that the colloidal state depends solely upon two factors, — 

 insolubility and the size of the particles. In reality there is but one 

 factor determining the colloidal state, namely, the mass of the granule, 

 for if a substance suspended in a liquid remains in a granular condition 

 it is insoluble. 



The colloidal state does not begin suddenly with a certain mass, to 

 end as suddenly when an upper limit is reached. There is a gradual 

 transition of the properties of the molecular state (solutions) into those 

 of the solid state (precipitates), and between these two extremes the 

 colloidal state is to be found. 



Considering only those substances immersed in water, which is the 

 general case in biology, one might say that the colloidal state becomes 

 manifest when the mass of the particle immersed is such that it is sub- 

 ject to brownian motion. With organic particles this takes place when 

 the particles reach a diameter of from 1 to 2;u, and this property becomes 

 accentuated as the diameter diminishes, being particularly marked when 

 the diameter reaches a point between 100mm and 1/xm- 



It may be well to state that the nature of the substance forming the 

 granules is of no consequence, nor is it of significance whether the particle 

 is living or dead. The sole factor is the mass; if it is sufficiently small 

 the particle becomes a colloidal "micella."t 



* I know, however, of some experiments, as yet unpublished, made at the 

 Institute of Delft (Holland), involving centrifugation at high speeds, that have 

 given results which confirm those reported here. 



t The water containing these mineral or organic bodies in suspension is the 

 intermicellar fluid. Fluids other than water are not considered here for they 

 are of no interest to biologists. 



