144 Dr. Baird on Entozoa, or Intestinal Worms. 



" in every microscopical point of matter, and every visible fila- 

 ment of which the whole animal or vegetable texture consists." 

 " I suppose," he says, " all semen, of any kind, to be an exalted 

 portion of animal or vegetable matter, secreted from the aliment 

 of every generating subject when it is adult, and no further de- 

 mand is made for its increase and growth ; this I suppose to be 

 endowed with a proportionable vegetative force ; to be various in 

 various circumstances, and heterogeneous in different subjects ; 

 but to be uniform in its productions when it falls into a matrix, 

 where it finds matter to assimilate of a quality or quantity suffi- 

 cient to form that specific being*." This vegetative force he 

 applied to account for the origin of Entozoa also. 



At the time Needham was advocating his peculiar views upon 

 this subject, Buffon was expounding a different theory. Animals 

 and plants he conceived to be formed by a particular combina- 

 tion of organic molecules. " These he supposed, by coalition, 

 to constitute the prima stamina of all animal and vegetable 

 bodies, simple, uniform, common to all, and consequently to be 

 found in a certain quantity in every portion of food, aliment, or 

 nutritive juice ; and from thence to be digested, and when the 

 subject became adult, secreted and strained, for the formation of 

 the seed of every plant or animal ; and in this fluid or substance 

 to be consequently found in much abundance. He further sup- 

 posed these original parts to be moving when disengaged, living 

 in appearance, and gifted with certain organs, but extremely 

 simple in their composition-}-." 



These theories have long been exploded. But though the 

 labours of Harvey, Spallanzani, and many other naturalists who 

 have succeeded them, prove incontestably that all animals, as far 

 as our observations can as yet carry us, have their origin from 

 ova or pre-existing germs, it must be confessed, that the intro- 

 duction of ova into such situations as those in which we discover 

 many Entozoa is exceedingly difficult to be accounted for. It 

 would appear, from some of the experiments of Spallanzani upon 

 Infusory Animalcules, that it is most probable that the ova or 

 germs of some of these curious little creatures can sustain a great 

 degree of heat, even boiling, for a certain space of time. If this 

 be correct in regard to Infusoria, it may be equally true with 

 Entozoa; and thus it is possible their eggs may be conveyed 

 alive into our stomachs with our food. Steenstrup has some 

 curious observations upon the method in which intestinal worms 

 can insinuate themselves from without into the internal organs 

 of the animals in which they are parasitic. In his experiments 



* Needham, Observations upon the Generation, &c. of Animal and 

 Vegetable Substances, p. 49. 

 t Needham, /. c. p. 20. 



