VIII. VIRUSES AND INSECTS 181 



vating agent, whereas normal structure is stable in its absence, a 

 view which will be dealt extensively in Part V. 



3. Heritable Changed Structure 



Although the reversible character of protoplasm-protein structure 

 is generally revealed in such a remarkable way, profound distortions 

 given rise to in the structure may render the recovery of the ori- 

 ginal structure extremely difficult. According to the structural 

 pattern of virus the degree of distortion which will be raised in the 

 protoplasm may vary, and some viruses can induce most profound 

 distortions, while others only slight changes. If the distortion 

 is slight, the distortion or the changed structure may be unstable, 

 and the original structure may be promptly recovered with the 

 disappearance of the virus and thus the disease will be cured, 

 whereas if the change is striking the changed structure may be stable, 

 and the virus will persist in the host cells as long as the host 

 exists. Thus when a host is affected by a strong virus it may be 

 unable to become freed from the virus for the remainder of its life. 



In connection with this trend of thought an extremely important 

 argument should be advanced. Strong viruses may thus be able to 

 induce replicas in host firm enough to remain for the host's life. In 

 the opinion of the writer, if the template action of the viruses is 

 still stronger, the change can be spread even into the germ cells 

 through which the structure is transmitted to the offspring. Such a 

 transmission of the virus structure to the offspring must be the 

 transmission of the virus itself to the offspring through the germ 

 cells. Now we shall see next the verity of this concept. 



It seems that the virus structures multiplying in insects commonly 

 disappear sooner or later, yielding to the normal structures. It has 

 been known, however, that sometimes viruses persist not only for the 

 remainder of the host lives, but also can be transmitted to the pro- 

 geny of the host. Fukushi (96) has found that the virus of dwarf 

 disease of rice was passed from parent to offspring to the third 

 generation without recourse to a fresh source of virus. Black (97) 

 likewise has confirmed che transmission of the clover club-leaf virus 

 from parent to offspring. He found that the virus can be inherited 

 over a period of four years without the insect coming to contact 

 with a fresh source of virus. Such hereditary transmission of viruses 

 has been recorded also with animal viruses. The eggs of a kind of 

 wood ticks apparently give rise to infective nymphs if the parent 

 tick is infected with the virus of equine encephalomyelitis. Similarly, 



