DlseEMBEE 26, 1919] 



SCIENCE 



5933 



eggs develop. A fruitful field for investiga- 

 tion is open in this direction. 



A. G. Huntsman 



CONSTANTS AND VARIABLES IN BIOLOGY 



To THE Editor of Science: I have read Mr. 

 Frank J. Kelly's letter on the substitutes for 

 the words " homozygous and heterozygous." 

 His argument appeals to me very particularly 

 because we are constantly confronted with 

 variously constructed new terms to express 

 scientific theories. It seems to me it is by far 

 best to give a special and restricted meaning 

 to the ordinary words of the English language 

 as is done in mathematics. 



In this science the word "constant " is used 

 to express a stable quantity and "variable " 

 one that is subject to change. Why could not 

 these two terms be bodily lifted from mathe- 

 matical language into biological? The second 

 term would quite adequately cover what Mr. 

 Kelly calls "inconstant form." 



J. E. DE LA JORRE BuENO 



SCIENTIFIC BOOKS 



Animal Parasites and Human Disease. By 

 Asa C. Chandler, M.S., Ph.D., Instructor 

 in Zoology, Oregon Agricultural College, 

 Corvallis, Oregon, xiii -\- 570 pages. 6X3. 

 254 figures. Cloth, $4.50 net. 

 The work aims to present the subject of 

 parasitology and especially its relations to the 

 problems of human disease in such form as 

 to make it attractive to the generally edu- 

 cated reader, and also useful to those less, 

 technically trained persons who have reason 

 to utilize information in this field. The 

 author's efforts have certainly achieved a good 

 measure of success. His style is attractive 

 and his presentation clear and reasonably 

 complete. The work will be used by many 

 who would not be inclined to refer to a more 

 extended and more critical presentation of 

 the subject. 



After an introduction, outlining the sig- 

 nificance of the subject and a discussion of 

 parasitism in general, the first part of the 

 work is devoted to a consideriation of protozoa. 

 These organisms have beeii grouped according 



to their systematic relationships. Under each 

 heading, however, the particular organism is 

 treated with reference to its significance in 

 producing disease. The chapters included in 

 this part are entitled: Introduction to Pro^ 

 tozoa, Spirochsetes, Leishman Bodies and 

 Leishmaniasis, Trypanosomes and Sleeping 

 Sickness, Intestinal Flagellates and Ciliates, 

 Amebse, Malaria, Other Sporozoa, and Ob- 

 scure or Invisible Parasites. 



This is the largest and certainly the most 

 valuable part of the work, for it brings to- : 

 gether a mass of material not readily avail- 

 able in this form in any other work. It 

 points out in striking fashion the significance 

 of recent discoveries concerning protozoa and 

 disease. On the whole the treatment is well 

 balanced and there are no important omis- 

 sions. The author has included studies of 

 recent date and perhaps has gone to the 

 extreme in giving a place to discoveries so 

 recent that their significance might well be 

 considered doubtful, even if the observed 

 facts are conceded to be correct. As an ex- 

 ample of this may be cited the entry, in a 

 note at the end of the chapter on spirochsetes, 

 of a discovery of one of these organisms in the 

 kidney in cases of typhus and the comment 

 that certain other bodies possibly are stages 

 in the life history of the organism. One may 

 reasonably doubt whether such conjectures 

 regarding a complex and difficult field are 

 really in place in a brief discussion intended 

 to give the general reader clear and correct 

 views of the present status of knowledge on 

 these questions. It is only necessary to recall 

 the number of organisms that have been at 

 times supposed to be " causes " of certain dis- 

 eases to see the questionable advisability of 

 listing such suggestions before they have been 

 thoroughly tested by other investigators. 



Part II. on the "Worms can not be regarded 

 as equally successful. The chapters included 

 in this part are entitled: Introduction to 

 the "Worms," The Flukes, The Tapeworms, 

 Hookworms, Other Intestinal Roundworms, 

 Trichina Worms, Filiarise and Their Allies, 

 Leeches. 



The material called for here is really better 



