BIOLOGY AND ZOOLOGY 129 



preparation of such records, and yet the complaint is sometimes made that by. inad- 

 vertence, or even by want of appreciation, important contributions are overlooked. 



In the following survey of the principal new points of substantial interest that 

 deserve attention since the completion in 1910 of the various articles on Zoological 

 subjects in the Encyclopaedia Britannica, it is only possible to select amid a mass of 

 detail, and to dwell on the questions of salient contemporary importance to the world 

 at large. Many details appropriate for the consideration of the technical specialist 

 are necessarily here passed over; for him, in his own subject, it would be impossible 

 to select and reject. Similarly it would be superfluous to include here any of the 

 technical descriptive matter relating to new species, mere extensions of known facts 

 in anatomy, embryology and morphology and such subjects as. would require elaborate 

 exposition. The attempt is, however, made to pick out what|; has seemed to be the 

 opening of new subjects, to modify in any important way the general conceptions 

 of the zoologist, or to show the tendency of developing scientific opinion. 



Protozoa. . 



Chlamydozoa. One of the most remarkable additions to knowledge, or perhaps, 

 it would be safer to say, to zoological theory, is associated with the name " Chlamy- 

 dozoa," which has been given by S. von Prowazek to a highly problematical set of 

 minute organisms, believed to be the cause of certain diseases in man and animals. It 

 is well known that since the relation between disease and the semi-vegetable organisms 

 termed bacteria 1 was discovered, a very large number of different diseases have been 

 traced to definite microbes belonging to that group, and the full life-history, mode 

 of infection and propagation and so forth have been worked out. More recently still, 

 the importance of parasitic Protozoa as the cause of many diseases,:such as malaria and 

 sleeping sickness, was discovered. Next came knowledge of the part played by the 

 slender thread-like Spirochaetes, which are frequently transported by blood-sucking 

 ticks, and which cause special diseases such as some of the relapsing fevers, whilst 

 others, like the spirochaete of syphilis, discovered by Schaudinn, pass direct from case 

 to case. There remained, however, certain diseases such as vaccinia and variola, 

 hydrophobia, scarlet fever, measles and foot-and-mouth disease, for which an organic 

 cause seemed certain but had not been identified. 



The supposed Ghlamydozoa are smaller than any known bacteria; the virus con- 

 taining them passes through ordinary bacterial filters, so that they must be studied 

 by different methods, and elude safeguards that are efficient with other microbes. They 

 are characteristically parasites of cells, living in the general cytoplasm, or in the nucleus, 

 and stimulating the formation of special reaction-products of the cells they infest. 

 They have a peculiar mode of multiplication, not splitting, like bacteria, by simple 

 fission, but forming an elongated dumb-bell shaped figure. They have not yet been 

 successfully cultivated, but artificial infections have been made from filtrates contain- 

 ing these bodies and not containing bacteria. So far they have been studied only in 

 relation to disease, and even in this respect it cannot be said that their existence and 

 properties have been definitely established. The work relating to them, however, is 

 very promising, and appears to open a new subject of much practical and theoretical 

 importance. If they are real entities, it is more than possible that they will be found 

 living as free organisms as well as parasitically. They would represent the lowest 

 known form of living being; they are certainly not cells, but are in a lower stage of 

 organic evolution. 



Spirochaetes. Dr. H. M. Woodcock, in dealing with Trypanosomes in the .E. B. 

 (xxvii, 340 et seq.), discussed the affinity of the Spirochaetes with those organisms, 

 and although admitting that there were reasons for the association, was disposed to 

 be sceptical about it. Later work has confirmed his doubts. Some observers, such as 

 Doflein, incline to regard them as a group transitional between bacteria and the Fla- 

 gellata (E. B. x, 464 et seq.); others, as closely related to the Oscillatoriae amongst 



1 See E. B. iii, 156 et seq.; also "Parasitic Diseases," E. B. xx, 770 et seq. 



