344 



SCIENCE. 



[N. S. Vol. XII. No. 296. 



brief, as it should be for the beginner ; and the 

 details of the treatment have been carefully 

 thought out and clearly written. The result is 

 probably as satisfactory a student's text as we 

 have. 



But a general comment in conclusion seems 

 to be called for. Many people like to have 

 their thermodynamics developed as a sort of 

 sub-topic of the theory of ideal gases. They 

 appear to think it suitable that one of the most 

 beautiful and wide- reaching branches of phys- 

 ical theory should be developed largely from the 

 properties of bodies that exist only in the imag- 

 ination. In the reviewer's opinion, this pro- 

 cedure is neither necessary nor wise. There 

 are two ways in which an exposition of theo- 

 retical thermodynamics can be written. One 

 can reach the absolute temperature and the 

 entropy from the properties of ideal gases, as 

 Professor Buckingham has done ; or he can 

 arrive at these functions from fundamental 

 physical postulates. The latter method reaches 

 true results from true premises ; while the 

 former jumps to true results from untrue prem- 

 ises. The latter method, properly worked out, 

 is fully as easy of comprehension as the former ; 

 and it gives a broader view : for it parallelizes 

 the thermodynamic temperature with other po- 

 tentials, and the entropy with other quantity- 

 co-ordinates ; and it brings out the distinction 

 between forces and potentials, and between 

 spaces and quantity-co-ordinates. As a plain 

 matter of fact, the theory of thermodynamics of 

 the present day is a symmetrical mathematical 

 analysis of the general problem presented by a 

 small number of inductively established pos- 

 tulates ; and, in consequence, it cannot be 

 grasped until it is comprehended as a logical 

 system of mathematically developed theory. 

 J. E. Trevok. 



Microorganisms and Fermentation. Ry Alfred 



JORGENSEN. Third edition. Translated by 



Alex. K. Miller and A. E. Lennholz. 



The Macmillan Co. Pp. 318. 



A practical knowledge of the phenomena of 



fermentation has been possessed by man from 



time immemorable. Until the present century, 



however, this knowledge has been purely an 



empirical one, the real cause of the phenomenon 



not being suspected. The present century has 

 seen the development of the subject from a 

 scientific standpoint, until to-day our knowledge 

 of the process of fermentation is thoroughly 

 systematic and based upon accurate experimen- 

 tation. The development of our present knowl- 

 edge upon the subject is properly divided into 

 three periods. The first was that of the indefi- 

 nite work of the early decades of the century, 

 when Schwann and others were demonstrating 

 that fermentative processes were closely related 

 to the life activity of microorganisms. The 

 second period was dominated by the revolu- 

 tionary work of Pasteur. Under his influence 

 not only was it demonstrated that fermentations 

 were caused by microorganisms, but various 

 types of fermentation were recognized and 

 found to be produced by diflerent species of 

 microorganisms. Under Pasteur's influence the 

 microscope came to be an aid to the fermenta- 

 tive industries and many a valuable practical 

 method was suggested and applied to the fer- 

 mentative processes. The third period has been 

 the most fruitful in results and in many respects 

 the most important. This period has been 

 dominated by Hansen, of Copenhagen. So 

 valuable has the work of Hansen been to the 

 brewing industry that a large brewery of Copen- 

 hagen has erected for his use one of the best 

 equipped laboratories in Europe, designed both 

 for practical experiments and for pure scientific 

 investigation. This third period of discovery 

 has been dominated by the invention of methods 

 of procuring absolutely pure cultures of yeasts. 



There is no one better able to write an ac- 

 count of the relation of microorganisms to fer- 

 mentation than the author of this work, who 

 lives in close relation to Professor Hansen, and 

 if his presentation of the subject is possibly 

 unduly influenced by Hansen's work it is 

 not to be wondered at. The fact is that the 

 whole subject of fermentation has been entirely 

 changed in the last two decades as a result of 

 the study of the strictly pure cultures obtained 

 by Hansen's methods. The earlier theories of 

 fermentation have given place to the theory 

 that fermentations are the results of enzymes 

 produced by microorganisms. The knowledge 

 of the yeast organism has been completely 

 changed as the result of the study of pure cul- 



