X. THE SUMMARY OF PART II. 119 



tion of a phage and the disintegration of the bacteria, the lysis, which 

 may be caused by a change of the protoplasm due to the virus disrupt- 

 ing the mutual association of elementary bodies. 



It is found that the rate of change in the blood cell is roughly 

 proportional to the concentration of a haemolytic agent, showing that 

 the protoplasm undergoes a change which tends to be directly propor- 

 tional to the amount of the haemolytic agent combining with the cell. 

 Also in the case of a virus and its host cell, the degree of influence of 

 the virus upon the host cell is apparently proportional to the number 

 of the virus particles adsorbed to it. Thus a weak virus fails to infect 

 the host cell when the number of the particles is small, but can get 

 the upper hand of the cell if many particles affect in union. 



Bacterial haemolysins, usually present in virus-like particles, may 

 affect the blood cells in the same way as viruses affect the host cells. 

 Thus, haemolysins may disturb the structure of the protoplasm of the 

 blood cell to cause a change which spreads throughout the cell ; as a 

 result the association between the haemoglobin and the protoplasm is 

 damaged leading to haemolysis. This change, however, cannot give 

 rise to so precise a rearrangement as to produce the very replica of 

 the haemolysin structure, so that haemolysins are not viruses. 



Viruses, like haemolysins, may sometimes disintegrate the proto- 

 plasm of host cells without producing the replica. If phage or influ- 

 enza virus particles are added to respective host cells in a great 

 excess, little or no virus is produced, although thereby the host cells 

 are injured severely. 



Since virus particles are no more than elementary bodies of proto- 

 plasm that have been liberated from the cell, their chemical com- 

 position should be similar to that of the protoplasm, mainly com- 

 posing of proteins and lipids. However, some plant viruses unlike 

 protoplasm are composed of proteins only. This presumably results 

 from the lipid elimination which might occur on the destruction 

 of the combination between protein and lipids due to the disturbance 

 by the virus. Such plant viruses are, therefore, isolated usually in 

 the form of particles which can be regarded either as lipid-free 

 elementary bodies themselves or as their split products, i. e., thinner 

 bundles or minute globular particles without lipids. 



Since thread-like protein molecules of the protoplasm may fail to 

 contract when lipids are eliminated, the plant viruses without lipid 

 may be bundles of protein threads. Usually hundreds of threads 

 appear to form a single bundle, whose length, therefore, must be the 



