770 REPORT—1899, 
Senile Decay and Rejuvenescence of Organisms. 
Another question, also of the utmost importance, confronts us at this point. 
As is well known, organisms are liable to wear and tear, sooner or later some part 
or parts essential to the maintenance of the vital functions wear out and are not 
renewed by the reparative processes which are supposed to be continually taking 
place in the organism. This constitutes what we call senile decay, and leads to the 
death of the organism. Asa good example of the kind of cause of senile decay, 
we may mention the wearing out of the teeth, which in mammals at any rate are 
not replaced ; the wearing out of the elastic tissue of the arterial wall, which is 
probably not replaced. There is no reason to suppose that the reparative process 
of any organism is sufliciently complete to prevent seniledecay. There is probably 
always some part or parts which cannot be renewed, even in the simplest organisms, 
Maupas has shown that this holds for the ciliated Infusoria, and he has also shown 
how the renewal of life, which of course must be effected if the species is to con- 
tinue, is brought about. He has shown that it is brought about by conjugation, 
during which process the organism may be said to be put into the melting-pot and 
reconstituted. For instance, many of the parts of the conjugating individuals are 
renewed, including the whole nuclear apparatus, which there is every reason to 
believe is of the greatest importance to living matter. 
On reconsidering the life of the Metazoa in light of the facts established by 
Maupas for the Infusoria, we see that all Metazoa are in a continual state of 
fission, as are the ciliated Infusoria. They are continually dividing into two 
unequal parts, one of which we call the parent and the other the gamete. The 
parent Metazoon must eventually die; it cannot be put into the melting-pot; its 
parts cannot be completely renovated. The gamete can be put into the melting- 
pot of conjugation, and give rise to an entirely reconstituted organism, with all the 
parts and organs brand-new and able to last for a certain time, which is the 
length of life of the individual of the species. 
Is there any other way than that of conjugation by which an organism can 
acquire a complete renewal of its organs? Is the renewal furnished by the 
development of all the parts afresh which takes place in a parthenogenetic ovum 
such a complete renewal? This question cannot now be certainly answered, but 
the balance of evidence is in favour of a negative answer. And this view of the 
matter is borne out by a consideration of the facts of the case. In all cases of 
conjugation which have been thoroughly investigated, the nuclear apparatus is 
- completely renewed. It would appear indeed as though the real explanation of 
the uninuclear character of the Metazoon gamete is to be sought in the necessity 
of getting the nuclear apparatus into the simplest possible form for renewal. Now 
in the development of a parthenogenetic ovum the ordinary process of renewal 
of the nucleus is often in partial abeyance. As avrule it only divides once instead 
of twice, and there is, of course, no reinforcement bynuclear fusion. It is, of course, 
possible that the reinforcement by nuclear fusion which occurs in conjugation may 
have a different explanation from the nuclear reconstitution which takes place in 
the formation of polar bodies and similar structures. On the other hand, it may 
all be part of the same process. We cannot tell. So that we are unable to 
answer the question whether for complete rejuvenescence a new formation of all 
parts of the organism is sufficient, or whether a reconstitution of the nuclear 
apparatus of the kind which takes place in the maturation of the Metazoon 
ovum and the division of the micro-nucleus of Paramecium is also required; or 
finally, whether in addition to the latter phenomenon a reinforcement and 
reconstitution by fusing with another nucleus is also necessary for that complete 
rejuvenescence which enables an organism to begin the life cycle again and to pass 
through it completely. 
With regard to buds in plants there is reason to believe that they share in the 
owing old of the parent. That is to say, if we suppose the average life of the 
individual to be 100 years,a bud removed at 50 will be 50 years of age, and 
only be able to live on the graft for 60 more years, 
