204 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii 



work of Pasteur. J. T. Needham's books, New Microscopical Dis- 

 coveries of 1745 and Observations upon the generation, composition, and 

 decomposition of animal and vegetable substances of 1 750, exercised a con- 

 siderable influence. They were written after the French fashion 

 (Needham had been educated at Douai) very concisely, and with 

 some brilliance of style, and it is hardly true to say, as Radl does, that 

 their experimental foundation was meagre. That it was inadequate 

 was proved definitely as events turned out by Spallanzani. De 

 Kruif 's account of the controversy is false and misleading, especially 

 in its estimate of Needham who is much more truly described in 

 the words of Louis Pasteur (see also Prescott). 



Needham's case rested upon the statement that, if meat broth was 

 placed in a sealed vessel and heated to a high temperature so that 

 all life was destroyed in it, it would yet be found to be swarming 

 some days later with microscopical animals. All depended, therefore, 

 upon the sureness with which the vessel had been sealed and the 

 efficacy of the heat employed to kill all the animalcules initially 

 present, and, in the ensuing controversy, Needham lost to Spallanzani 

 entirely on a question of technique. It may be remarked here, with- 

 out irrelevance, that the problem is still unsolved; for all that was 

 proved by the experiments of Spallanzani was that animals the size 

 of rotifers and protozoa do not originate spontaneously from broth, 

 and all that was proved by those of Pasteur was that organisms the 

 size of bacteria do not originate de novo in that way. The knowledge 

 which we have acquired in recent years of filter-passing organisms, 

 such as the mosaic disease of the tobacco-plant, and phenomena such 

 as the bacteriophage of Twort and d'Herelle, has reopened the whole 

 matter, so that of the region between, for example, the semi-living 

 particles of the bacteriophage (lO"^^ gram) and the larger sized 

 colloidal aggregates (io~^^ gram) we know absolutely nothing. The 

 dogmatism with which the biologists of the early twentieth century 

 asserted the statement omne vivum ex vivo was therefore, like most 

 dogmatisms, ill-timed. 



But to dwell further on this would be a digression. The important 

 point was that Spallanzani's victory was a victory not only for 

 those who disbelieved in spontaneous generation, but also for those 

 who believed in the preformation theory of embryogeny. By 

 1 786, indeed, that viewpoint was so orthodox that Senebier, in his 

 introduction to an edition of Spallanzani's book on the generation 



