1^4 Appendix. 



Though not pertuient, strictly speaking, to a historical 

 sketch like this of the doctrine of spontaneous generation, it is 

 interesting to know what are the organisms whose germs can 

 withstand such savage treatment as that described, and whose 

 mode of generation is involved in any obscurity. They are only 

 b^d very lowest orders of life known, and by common consent 

 the question is limited to the Monas, Vibrio, Spirilla and Bacti- 

 rium. The last three are generally conceded to belong to the 

 vegf^table world. At all events, they stand upon the extremest 

 limits of that debatable ground in which spontaneous generation, 

 if it is ever shown to be a reality, must be found. The higher 

 orders, comprising almost the entire class of infusoria, are now 

 known to reriroduce themselves by true sexual generation.* 



The last, but by no means most unimportant contribution 

 to this subject is by Prof. Tyndall ; and I cannot close this 

 sketch without alluding to his work, although it was not under- 

 taken for the purpose of solving or attempting to solve the prob- 

 lem of spontaneous generation. His investigationsf were a con- 

 tinuation, practically, of his former experiments on floating par- 

 ticles in the air (to whi(!h allusion has already been made, p. 162), 

 and were for the purpose of supplying direct evidence to connect 



* The observations of stein, Englemann, Balbianiand others have clearly 

 established this fi\ct for a large share of the infusoria. Their labors have been 

 supplemented and their results corroborated by the elaborate studies of Ernst 

 Eberhard. An abstract of his work may be found in Quar. Jour. Micros. iSci. 

 New iSeries, Vol, VIII, p. 155. See Dalton, loc. cii. for reference to Stein and 

 others. 



t Medical Times and Gazette, January 29, ISTO. Also the ianeei, same date. 

 The title of his paper is "On the Optical Deportment of the Atmosphere in 

 Reference to the Phenomena of Putrefaction and Infection." An abstract by 

 the author himself was published in Nature, February 3, 1876. 



Since this lecture was given Dr. Bastian has sharply criticised both Tyn- 

 dall's experiments and his deductions. In turn Prof. Tyndall has made a re- 

 joinder of equal positiveness and severity. Dr. B. entitles Tyndall's paper 

 "a new attempt to establish the truth of the germ theory," and then un- 

 sparingly attacks not the germ theory of disease but the doctrine of bio- 

 genesis—questions which are far from being identical. A most dispassionate 

 review of Dr. Bastian's position in this controversy may be found in the 

 Popular Science Review, 1S76, in a paper by Rev. W. H. Dallinger, V.P.R.M.S. 

 This paper contains also some valuable discoveries made by the author 

 and Dr. Drysdale. 



