April 28, 1905.] 



SCIENCE. 



669 



Laboratory Supply Company is now making 

 some of these instruments to serve as re- 

 versible stereoscopes. In their manufacture 

 the difficulties of projection of the two images 

 to differently situated planes have been en- 

 countered, and have been met only by reducing 

 this to a minimum and counting upon the 

 fortunate property of the eyes to ignore or, 

 indeed, to make terms of peace with this dis- 

 crepancy. I find that this is easy, when an 

 ordinary photograph with no sharp gradations 

 of light and shade is used; but with diagrams 

 the non-correspondence of top and bottom is 

 moderately disturbing. I have not hesitated 

 for purposes of convenience to combine lenses 

 with this reflecting stereoscope; but I shall 

 profit by Professor Whitman's suggestion to 

 see how far the increased proximity of the eyes 

 to the mirrors, which he recommends, will 

 obtain certain of the advantages which I tried 

 to secure by weak lenses. This last variation 

 is a detail of construction in which Professor 

 Whitman's device differs from mine. 



Joseph Jastrow. 

 U?fn'ERSiTY OF Wisconsin, 

 April 8, 1905. 



SPECIAL ARTICLES. 



A REVISION OF THE COCCACE/E.* 



The classification of the bacteria presents 

 peculiar difficulties for several reasons. Mor- 

 phological distinctions are so slight that phys- 

 iological characters must necessarily be in- 

 voked in order to separate and classify the 

 various organisms, and these physiological 

 characters are often variable. Pathogenicity 

 may be taken as a type of those powers of the 

 organism which are easily and profoundly 

 modified by external conditions. On the other 

 hand, there are numerous characters which ap- 

 pear to be extremely constant. Such minute 

 differences as occur in the resistance of dif- 

 ferent races to unfavorable conditions often 

 remain unchanged through long periods of cul- 

 tivation. In using these constant characters 

 for classification we are met by another diffi- 

 culty. Though constant, the differences are 



* Preliminary communication. From the Bio- 

 logical laboratories of the ^Massachusetts Institute 

 of Technology. 



very minute, and in studying a number of 

 organisms a perfect gradation is often found 

 between the widest extremes. This is ex- 

 actly what should be expected from organ- 

 isms which reproduce only by asexual methods 

 since it is the fusion of independent cells 

 which swamps minor differences producing 

 the uniformity of species among higher plants. 

 With asexual reproduction every minute varia- 

 tion which is inheritable must persist un- 

 changed until some other chance variation 

 occurs. Each such variation means a new 

 and different type of bacterium. 



The immense number of generations which 

 may succeed each other in a short space of 

 time makes boundary lines as shifting as they 

 would become among the higher plants if a 

 dozen geological epochs were considered all at 

 once. 



Since with unicellular organisms acquired 

 characters may probably be inherited in a 

 higher degree than with other forms, existing 

 races of bacteria will be markedly influenced 

 by the selective effect of environmental con- 

 ditions, and must bear the impress of their 

 recent history. 



There are, therefore, no species among the 

 bacteria in quite the sense in which we or- 

 dinarily use the word, — as indicating a group 

 of individuals bound together by a number of 

 constant characters and easily identified by 

 mutual fertility. From one point of view 

 each distinct race might be considered a spe- 

 cies; but to apply a name for every grade of 

 difference in each varying character would 

 be impracticable; and such names could have 

 no true specific value. The best solution of 

 the difficulty is the establishment of certain 

 types around which the individual organisms 

 may be more or less closely grouped; but it 

 must be clearly recognized that the groups 

 thus formed are defined by relation to the 

 type at their center and are not sharply 

 marked off at their extremities from the other 

 groups adjacent. 



It is impossible to make a natural classifica- 

 tion of the bacteria, which shall be a true ex- 

 pression of phylogeny by considering a single 

 character at a time, — for example, by dividing 

 a group dichotomously, first according to mor- 



