738 
DR. CARPENTER ON THE MUTUAL RELATIONS OF 
This inference derives a remarkable confirmation from a series of facts, which indi- 
cate that when that specialization of function takes place, which has been mentioned 
as a characteristic of the higher organisms, the cells which become the instruments 
of some one particular kind of operation seem to lose their other endowments, — as if 
the expenditure of the vital force of each cell upon any one purpose, unfitted it for 
any other agency. Thus the assimilating cells (whether floating in the nutrient fluids, 
or included in the absorbent glandulse), whose function it is to convert the raw material 
supplied by the food into organizablepZa^ma, exercise little or no purely chemical trans- 
formation ; they do not undergo change of form ; they do not exert any mechanical 
or nervous power; and they do not reproduce their kind. So, again, the cells which 
are specially endowed with the power of multiplication, seem to possess no other spe- 
cial vital endowment; simply receiving the nutriment which has been prepared for 
them by other agencies, and applying it to the production of new cells, which, if 
themselves possessed of more special endowments, do not reproduce themselves. Of 
this we see an example in the first development of the embryonic structure, the cells 
of which rapidly multiply by the process of fission, up to the time at which histological 
transformations commence, and then this multiplication almost or entirely ceases; so 
that (as in the case of tlie insect, Avhose larva is an embryonic mass of very rapid 
production, composed almost entirely of cells destined to undergo histological change 
during the metamorphosis) the perfect structure may be even smaller than that from 
which it is developed. In the formation of new parts which make their appearance 
at a subsequent time, the same rule generally holds good, viz. that their foundation is 
laid in a mass of cells which rapidly multiply up to a certain point without histo- 
logical transformation, and then undergo histological transformation with little further 
multiplication. But the most striking illustrations of this principle are perhaps to be 
derived from those cases, in which a continual production of cells possessed of some 
special endowment goes on during adult life. Thus it is necessary for every act of 
secretion, that a new formation of secreting cells should take place within the ultimate 
follicles of glands. These ultimate follicles are really to be regarded (as shown by 
Prof. Goodsir*) in the light of parent-cells, which produce the true secreting cells 
in proportion as the materials of their growth are supplied by the blood. Now these 
parent-cells themselves possess no secrethig power, their vital force being entirely ex- 
pended in the production of the true secreting cells. On the other hand, the true 
secreting cells possess no reproductive power, but die and are cast off when they have 
reached their maturity ; as if their whole vital force were expended in the secreting 
process, which is itself nothing else than a portion of the act of growth. This will be 
found, the author believes, to be the type of a large order of facts, of which some 
others will be presently noticed. Again, the cells which are endowed with the spe- 
cial reproductive pow'er, exercised in the true act of generation, seem to possess no 
other endowment ; they do not exercise chemical transformation, nor do they undergo 
* Anatomical and Pathological Observations, No. V. 
