IV. THE VARIABILITY OF VIRUSES 161 



In emphasizing of the virus individuality Schutz (74) stated that a 

 striking feature of viruses is their heterogeneity when considered as 

 a group. They are "individualist". They are not like in their resist- 

 ance to heat, cold, drying, hydrogen ion concentrations, organic or 

 inorganic chemical compounds or to the action of individual enzymes. 



The occurrence of such a variation, however, seems to be a com- 

 mon feature of protein molecules, not being confined to virus particles 

 only. There are a vast number of evidences that each molecule of 

 proteins, such as toxins, antibodies, and enzymes, has each individu- 

 ality. 



It has been sometimes claimed that living matters are distinct 

 from non-living matters in their variability as well as in their multi- 

 plicability. The variability, however, is merely a property of pro- 

 teins, by no means a characteristic of living matters. 



The individuality can be readily demonstrated with phage, for the 

 individual property of this virus is clearly seen in the property of the 

 plaques. Since a plaque is formed by a group of phages derived from 

 a single particle, the degree or manner of the damage of bacteria due 

 to the particle, derived from the single phage particle, is shown in it. 

 Thus a large plaque will show the great multiplicability of the parent 

 phage while a smaller plaque lesser multiplicability. If some parent 

 particle has the property to lyse the bacteria completely a plaque of 

 complete clearness will be obtained, whilst only a turbid plaque will 

 be raised by a phage group derived from a parent particle causing an 

 incomplete lysis. 



Owing to such properties of plaques, we can easily demonstrate 

 that even a phage sample, originated from a single particle, never 

 consists of uniform particles. Some workers have attempted to divide 

 phages affecting E. coli into several types, but it would be very sur- 

 prising if there was no gradual transition among them. 



The individuality of viruses is probably analogous to that of 

 higher organisms, but presumably because of the easy occurrence of 

 variation in viruses individual differences appear to be more distinct 

 in them than in higher organisms. Virus particles having such dis- 

 tinct individuality may undergo further variations which may vary 

 with each particle when exposed to various environmental effects. 

 Thus the divergency in the individuality will become still greater, 

 leading to the appearance of numberless strains. 



Jensen (75) has isolated over fifty strains of tobacco mosaic virus 

 from the yellow spots of the leaves. Some of these are apparently 

 similar to tobacco aucuba mosaic virus, a strain commonly found in 

 nature, but others differ from any strains previously described. Jensen 

 distinguished the various strains by the ease with which they infect. 



