90 



is by the force of its causes made independent of its original, and 

 capable of another stage of life. 



56. It will be found that this enumeration of changes agrees 

 with the changes which we observe. None of these textures are 

 at once perfected. As the textures are what the properties of 

 the organic spirit make them, so we infer from these mutations of 

 the materials previous mutations of the living principle, and these 

 are the most satisfactory grounds of the inference. 



57. The harmony of functions too is preserved in the same 

 way in all the stages of existence; it is preserved by internal rela- 

 tions, which only illustrate a principle of causation, stated at 

 38, &c. Chap. iii. Book 1. The relations of the ovum with the 

 mother, during the uterine connections, are next to be considered. 



58. The ovum having passed through the Fallopian tube 

 into the uterus, speedily acquires an attachment to this viscus, 

 by which an intercourse is still maintained between the mother 

 and the offspring. It is not necessary, as has been before shewn, 

 that any properties of the organic spirit should be conferred by 

 the mother on the ovum at this stage. This conclusion is princi- 

 pally deduced from the phenomena of the crustaceous ova, which 

 are developed into the future animal without any vascular inter- 

 course with the mother, or, in some instances, without an inter- 

 course of any other kind, between the periods of their escape 

 from the ovaducts and their final maturation. 



59. But although it is not necessary that the ovum should ac- 

 quire the vital properties in the stage we are considering, yet the 

 connection between the ovum and the mother is such that it cannot, 

 during this period, be dissolved without a cessation of the pheno- 

 mena which characterize the living principle in the ovum. We 

 find, also, that an arrangement, very similar, obtains with respect 

 to the crustaceous ova: thus, if the temperature of an egg is not 

 pretty equally maintained, or if a sufficient degree of heat is 

 withheld during the periods of incubation, the embryo, whatever 

 its present organization might be, dies. The facts, thus indicated, 

 appear to give the sanction of probability to the following infer- 

 ence, which is also supported by other facts to be stated subse- 

 quently, viz. 



60. As soon as the organic spirit of the ovum has ceased to 

 be a constitution of properties at rest; as soon as the ovum has 

 commenced the actions characteristic of life ; that then it is, from 

 the force of its own causes, disposed for death, or a return to its 

 separated constituents. It has been quaintly said that " life is a 

 forced state." I am disposed to say of it, with less quaintness, that 

 it is a constitution disposed to change its form ; that its present form 

 is maintained by certain agents, in the usual way of causation; 

 and that its changes also are accomplished according to the same 

 general law. The organic spirit itself tends to change its form, 

 and the textures follow its fate; such is the force of internal 

 causes: the force of some which are external is to preserve the 



