GENERAL CONCLUSIONS. 815 



built up ; and, that the chemical treatment to which they had been 

 subject, in their extraction from the atmosphere, would be likely 

 to destroy the vitality of fecund germs, if any were present. To 

 the alleged absence of any organisms in the experiments which 

 were calculated to exclude extraneous germs, and to unfit the 

 infusion for the development of any it might contain, the graver 

 objection applies, that the microscopic power employed by Pas- 

 teur in their search was insufficient. Dr. Child, 1 in experiments 

 which seem to be as exclusive as Pasteur's, does obtain bacte- 

 riums, discoverable, at first, by a power of 1,500 diameters, and, 

 once so seen, afterwards recognisable by a power of 750 diame- 

 ters : whereas Pasteur, in his quest, did not avail himself of a 

 power exceeding 350 diameters, and consequently failed to detect 

 the evidence of ( nomogeny,' under conditions as decisive as can 

 be hoped in an attempt to prove a negative. Against ' pan- 

 spermism,' or the dogma that animalcules of infusions come, in- 

 variably and exclusively, from pre-existing germs falling from 

 the air, Pouchet records the results of experiments, conclusive 

 or satisfactory from their simplicity and ease of repetition, and 

 freedom from need of minute, ambiguous, manipulatory precau- 

 tions. 2 



A glass tube containing a filtered infusion is placed in the 

 middle of a glass dish containing the same infusion : this stands 

 in a wider dish of water in which a bell-glass is placed covering 

 the vessels with the infusion. At the end of four or five days 

 the tube-infusion has a thick film abounding with ciliate infuso- 

 ria : the dish-infusion has a thin reticulate film containing only 

 bacteriums and other small non-ciliate 6 microzoaires.' It is 

 ( difficult to see how the germs of the one kind of creatures should 

 have entered or become developed in the one vessel and entirely 

 different kinds in the other.' 3 



I refer the reader to cccxn". and cccxxxv". for further ana- 

 lysis of the grounds of the disputants, and proceed to remark, 

 that the illustrations of the process of development of a Para- 

 mecium* so closely resemble those of the ovarian ovum in Fish 



V 



or Mammal, that either fig. 555 or fig. 416, vol. i. of the pre- 



1 cccxn". - cccx". pp, 122, 135. 



3 cccxn", p. 101: paraphrasing Pouchet : ' Si les ceufs tombaient de 1'atmosphere, 

 comme le preteudent les panspermistes, il n'y aurait pas de raison au monde qui 

 put faire que, dans la metne portion d'air, 1'eprouvette en soit constamment remplie et 

 la cuvette jamais. Celle-ci meme, a cause de sa surface bien autrement eteadue, 

 devrait en recolter infiniment plus.' cccx". p. 136. 



4 cccx". PI. II. figs. 1-5, and cccxi". PI. I. fig. 1 . 



