AIR-GERMS AND SPONTANEOUS GENERATION. 93 







whose ideas lie upheld. Soon after began the great controversy be- 

 tween Needham and Spallanzani, who refuted, by experiment, the 

 conclusions arrived at by Needham. 



The controversy turned principally on this point: Spallanzani was 

 not satisfied with heating the hermetically-sealed vessels containing 

 the infusions, for several minutes, merely the time which is required to 

 cook a herts-egg, and to destroy the germs, as Needham expresses it, 

 but he kept them for the space of an hour in boiling water. He then 

 observed no production of infusoria. But, objects the English ob- 

 server, from the manner in which he treated and put to the torture 

 his nineteen vegetable infusions, it is evident that he not only much 

 weakened, or perhaps totally destroyed, the vegetative force of the 

 substances infused, but also entirely corrupted, by the exhalations 

 and the odor of the fire, the small portion of air which remained in 

 the empty part of his vessels. It is not, therefore, surprising that his 

 infusions, thus treated, gave no signs of life. Such must necessarily 

 have been the case. This idea, that the action of the temperature of 

 boiling water destroys the vegetative force of infusions, is maintained 

 even at the present day, and has served as an argument to the hete- 

 rogenists ; as they were unable to attack the material correctness of 

 Pasteur's experiments, they did not accept the conclusions which he 

 sought to derive from them. 



We find also in the passage just cited, the necessity for the experi- 

 ments made by Schwann and Helmholtz on calcined air, and for those 

 of Schroder and F. Dusch, on strained air. The objection of a possi- 

 ble change in the air contained in the vial, under the influence of pro- 

 longed boiling, in presence of organic substances, was a serious one at 

 the time that it was brought forward ; it becomes more so, when we 

 know that the air confined over preserved meats, prepared by Ap- 

 pert's process, contains no oxygen. It was, therefore, absolutely ne- 

 cessary to place the infusions in contact with air in a normal condi- 

 tion, after that boiling had deprived them of their preexisting germs, 

 avoiding at the same time any new germs brought by the air. 



For this purpose, Dr. Schwann heated flasks containing the infu- 

 sions, until the destruction of the germs was insured; but his flask 

 was not closed : it communicated freely with the surrounding air by 

 mean of a glass tube bent in the form of a U, and heated, in one 

 part of its length, by means of a bath of fusible alloy. Under these 

 conditions, the air may be renewed in the flasks, but the fresh atmos- 

 pheric air admitted has undergone, like the infusion, the action of 

 heat, which destroys the germs. Schwann's experiment was very 

 decisive, as to broth made from meat ; and the negative result (no 

 development of infusoria) was quite satisfactory. But it was not the 

 same with analogous trials on alcoholic fermentation, which gave con- 

 tradictory results. Ure and Helmholtz repeated and multiplied these 

 experiments with the same success. 



