564 



NA TURE 



[October \, 190ft 



mental processes of anabolism, katabolism, and growth 

 as slow chemical reactions catalytically accelerated by 

 protoplasm and inevitably accelerated by temperature. 

 This soon follows if we once admit that the atoms and 

 molecules concerned possess the same essential properties 

 during their brief sojourn in the living nexus as they do 

 before and after. 



Perhaps the more real question is rather as to the 

 importance and significance of this point of view. Proto- 

 plasmic activity inight be something so much /)cv se, and 

 th."* other factors of the nature of stimuli might be super- 

 posed so thickly upon that substratum which should be 

 dominated by simple principles of chemical mechanics that 

 for practical purposes the operations of the latter would be 

 so overlaid and masked as to be negligible. .\ survey of 

 this field, however, seems to show that this is not so, 

 and that the broad action of the law of mass and the 

 acceleration of reaction-velocity by temperature are 

 obviously responsible for wide ranges of phenomena. 



Now the conception at the bottom of these principles is 

 that of reaction-velocity, and the conclusion of the whole 

 matter is that the physiologist must frankly take over 

 from physical chemistry this fundamental conception.' 

 Under definite conditions of supply of material and 

 temperature there is a definite reaction-velocity for a given 

 protoplasm, and the main factors that alter the rate of 

 metabolism, viz., heat, nutrition, and traces of impurities 

 are exactly the factors which affect the velocity of reactions 

 in vitro. 



Working on this basis we no longer need the vague 

 unL|uantitative terminology of stimulation for the most 

 fundamental of the observed " responses " to external con- 

 ditions. Three sets of phenomena we have observed 

 which, though usually treated in the category of stimula- 

 tion, draw a clearer interpretation from the conception of 

 reaction-velocity. These were : (i) the relation of develop- 

 ment to the absence or deficit of single essential food 

 constituents ; (2) the occasional striking effect of minute 

 traces of added foreign substances upon the whole rate 

 of growth and metabolism ; and (3) the general doubling 

 of the activity of vital processes by a rise of 10° C. 



The next higher stratum of principles should be the 

 complications introduced by limiting factors which inter- 

 rupt the extent of the manifestations of these principles 

 and by various correlations, as, for example, that by which 

 the reaction-velocity of one catabolic process might with- 

 draw the supply of material needed for full activity of 

 another different process. To this sort of relation may 

 be attributed that phenomenon so characteristic of the more 

 complex vital processes and quite unknown in the inorganic 

 world, namely, the optimum. 



Finally, superposed upon all this comes the first category 

 of phenomena that we are content still to regard as 

 stimulatory. From the point of view of metabolism and 

 reaction-velocity many of these appear very trivial, though 

 their biological importance may be immense. Think how 

 little the tropistic curvatures of stems and roots affect our 

 Quantitative survey ; yet a little re-arrangement of the 

 distribution of growth on the two sides of an organ mav 

 make the difference between success and failure, between 

 life and death. 



From our present noint of view vision does not extend 

 tn the misty conceptions of stimulation urmn our horizon. 

 We may therefore postpone speculation upon the 

 mechanical principles governing them and await the time 

 when bv scientific operations we shall have reduced to law 

 and order the intervening region, which we mav entitle 

 the chemical substratum of life. This done we may 

 venture to pitch our laboratory a march nearer to the 

 phenomena of protoplasmic irritability and make direct 

 attack iiDon this dominating conception, the first formid- 

 able bulwark of vital territory. 



_ 1 No general treatment of tlie nhysiolncA- nf plants has vet b-en attempted 

 in terms r.f reartion-velociiy. CVap-l;, however, in the introrlucion to his 

 stupendous " Biorhemie Her Pflanren." vol i., loos. does direct attenti"n to 

 th;- '•oneeptir.n of " reaction-velo-itv "and refer tn the st.nndard literature on 

 this subiect and on r.atalvsls. th"ueh direct annliratinn is not miidf to th» 

 plant. Cohen (" Physical Themistrv for Physicians and Rioloests," Enelish 

 eaition. igo:;) considers in detail some biological applications of the accelera- 

 tion 01 reactions by temperature. 



NO. 2031, VOL. 78] 



1 



THE SCIENTIFIC STUDY OF PLAGUE. 



n^IlE fourth extra number of the Journal of Hygiene, 

 containing the work of the Plague Commission, has 

 appeared lately.' Chapter xxvi. — the first of this number 

 — IS a translation of a St. Petersburg thesis (1904) by Dr. 

 Verjbitski, which has not been published beiore. The 

 Russian worker arrived independently at conclusions, with 

 regard to the transmission of plague by blood-sucking 

 parasites, which tally well with those of the Indian 

 workers. The common rat flea of Cronstadt, however, 

 is Typlilopsylta musculi, and appears not to attack man. 

 Experiments with bugs gave results similar to those with 

 fleas. 



Chapter xxvii. is the substance of a report submitted to 

 the Indian Government by Lieut. -Colonel Bannerman and 

 R. J. Kdpadia in 1904. It shows that domestic animals 

 (pigs, calves, fowls, turkeys, geese, and ducks) are not 

 susceptible to a general infection with B. pesiis, though 

 local abscesses were sometimes produced by inoculation. 



Chapter xxviii. gives some experiments on septicemia 

 in human plague, with others on the infectivity of excreta, 

 supplementary to work detailed in an earlier number of 

 these reports. 



The most interesting portion of this number is contained 

 in chapters xxix. to .xxxi., dealing with the bionomics of 

 fleas, the mechanism by means of which the flea clears 

 itself of plague bacilli, and the seasonal prevalence of 

 plague. 



Simple and ingenious are the methods of carrying out 

 flea experiments here described. The results, too, are 

 interesting. It is found that fleas do not remain constantly 

 on their host, but hop off on to the floor or into the nest 

 of the rat. Here the eggs are laid, and, when the fleas 

 seek food again, it is likely that a different rat will supply 

 the meal. In this way the same fiea may bite several 

 rats in the course of the day, and forms a very efficient 

 means of spreading infection. Not only this, but the 

 experiments prove that, where many rat fleas are present 

 (P. cheopi.'i), some of them will readily attack man, thougli 

 rats are at hand. 



The developmental stages of the flea are passed through 

 in three weeks in favourable circumstances. Temperature 

 above So° F. has a retarding influence, which becomes very 

 marked between 85° F. and 90° F. At these temperatures 

 fewer eggs are laid, and their development is slower than 

 at lower temperatures such as 70° F. 



Passing to the consideration of the seasonal prevalence 

 of plague, we find that though climatic conditions go for 

 something, yet they leave much to be explained. Charts 

 are given which show the recurrent plague epidemics in 

 six widely different localities, along with temperature and 

 humidity curves. Humidity appears to have little import- 

 ance. With regard to temperature, the following con- 

 clusions are drawn : — 



(i) A plague epidemic is checked when the mean daily 

 temperature passes above 80° F., and especially when it 

 reaches 85° F. or 90° F. 



(2) A mean temperature above So° F. affects the con- 

 ditions to which the plague bacillus is subjected in the 

 stomach of the flea. At high temperatures, about qo° F., 

 the plague bacilli disappear from the stomach of the flea 

 much more quickly than at lower temperatures, namely, 

 between 70° F. and 80° F. 



(3) A plague epidemic may, however, come to an end 

 when the temperature is most suitable. Other factors 

 must therefore be present in these cases. 



Reading further, we find these "other factors," tending 

 to check an epidemic, are a diminution in the number of 

 rat fleas, a diminution in the tot.al number of rats, and an 

 increase in the prooortion of immune to susceptible rats. 

 Perhaps the first of these factors is the least important ; 

 chart vii. shows that in Bombay, in 1907, the epizootics 

 (in both M. dcctimaniis and M. ratiiis), and even the 

 epidemic, began to decline a month before the fle.a infesta- 

 tion showed any decrease. 



The last two factors are consequences of the outbreak 



_t Reports on Plaeue Invest'gations in India. Journal rf Hv^'cne.^^. 

 viii.. No. 2. Pp. 148; Charts vii. Cambrdge: Univert^ity Press, May, 

 1908.) Price 6i. 



