June 1, 1895.] 



KNOWLEDGE, 



125 



Among the bacteria producing a blue colour on cultiva- 

 tion, the bacillus of " blue milk," B. ci/aiw<itnf):, is one of 

 the most typical. It is not au uncommon occurrence, 

 especially in parts of Gei-many, for milk, otherwise perfectly 

 normal, to assume a bright blue colour ; and before the 

 real cause was known, many theories were put forward to 

 account for the phenomenon. For instance, it was ascribed 

 by various observers to iron, indigo, and a diseased 

 condition of the cows ; while Henri Bracconat thought 

 it was due to spontaneous decomposition of the milk. 

 The bacillus which is now known as the cause is a motile 

 organism 3/x in length by -Jp in breadth. Grown in milk 

 it produces a slate-blue colour, changing to bright blue as 

 soon as the milk commences to turn sour. No coloration 

 occurs if the temperature be above 36^ C. According to 

 Erdmann the colouring matter is the same as the aniline 

 colour tii-phenyl-nrsaniline, but this is denied by Schroter. 

 In its physiological effect "blue milk" appears to be 

 harmless, and chickens have been fed for weeks on bread 

 soaked in it without being any the worse. 



The bacterium of " yellow milk," B. .nintJiinum, is an 

 interesting illustration of au organism producing a yellow 

 pigment. In boiled milk it gives rise to a bright yellow 

 coloration, which it also shows when grown on sterilized 

 potato. The colouring substance, which is very similar to 

 the yellow anihne colours, is soluble in water, but insoluble 

 in alcohol. The organism usually occurs in the form of 

 cocci, about 1/x in diameter. Green pigments are produced 

 by several species of bacteria, more than half a dozen of 

 which have been found in water. Of these. Bacillus 

 fluorescens liquefaciens occurs most frequently. It is of a 

 short rod form, l-5f4 long and O-ou. broad. When grown 

 on gelatine it causes the culture medium to assume a 

 beautiful fluorescent green colour, and at the same time 

 liquefies it. 



Eepresentatives of the other colours — violet, orange, 

 and brown — may also be found among those formed by 

 bacteria. According to Cohn and Schroter, who attempted 

 to classify them by their solubility in water, the red and 

 yellow substances are, broadly speaking, more soluble in 

 that liquid than the orange, green, and blue. In some 

 cases the colour is confined to the protoplasm and inter- 

 cellular substance of the bacteria, while in others ([•.,'/., the 

 " blue milk " bacillus) it spreads outside the cells on to 

 the culture medium. It would thus appear that some are 

 products of excretion, as well as of secretion, and all seem 

 to be formed through the decomposition of the nitrogenous 

 substance in which they grow. As to the part they play 

 in the physiology of the bacteria but little is known, and 

 the suggestion that they supply the place of chloroplujU in 

 plants does not throw much light on the question, since it 

 has not yet been proved beyond doubt what the function 

 of chlorophyll is. 



THE GIANT BIRDS OF SOUTH AMERICA. 



By E. Lydekkek, B.A.Cantab., F.R.S. 



FOR many years the minds of philosophical ornitholo- 

 gists have been much exercised by the problem of 

 the origin and phylogeny of the existing flightless 

 ostrich-like birds and their fossil relatives. Not 

 very long ago, we believe it was not an uncommon 

 opinion that all these Ratite birds, as ostriches, rheas, 

 cassowaries, and emeus are collectively called, were the 

 immediate descendants of a certain group of extinct reptiles, 

 and that they themselves gave origin to the flying birds. 

 One circumstance is, however, fatal to this hypothesis. 

 As most of our readers are probably aware, flying birds 



have the bones of the fore-limb, or wing, constructed on a 

 very peculiar plan, and quite unlike those of either 

 mammals or reptiles. But precisely the same type of 

 structure is presented by the rudimentary wings of such 

 of the ostrich-like birds as possess these appendages at all ; 

 and it is quite clear that if these birds had been evolved 

 from reptiles in the condition we now find them — that is to 

 say, without the power of flight — they would have retained 

 the reptilian type of fore-limb, and would not have an 

 aborted bird's wing. Hence it is clear that we must regard 

 the ostriches and their allies as the descendants of birds 

 endowed with the power of flight, but whose wings have 

 become gradually atrophied by disuse till, as in the emeus, 

 they are extremely minute, or, as in the extinct moas of 

 New Zealand, have even completely disappeared. Having 

 arrived at this satisfactory conclusion, the reader might 

 perhaps think that there was nothing more to be said on 

 the subject; but here, unfortunately for his peace of mind, 

 another problem presents itself for consideration. We 

 have, indeed, to decide whether all the Ratite birds have 

 sprang from an original flying ancestral stock, or whether 

 several flying birds have given rise to degraded flightless 

 types which have subsequently become so hke one another 

 as to form one apparently homogeneous group. 



So far as the existing and later Tertiary representatives 

 of these giant flightless birds are concerned, it does not 

 appear that we have at present any means of deciding 

 this question one way or the other. The discoveries 

 made during the last few years in the older Tertiary 

 deposits of Patagonia have, however, gradually brought 

 to light the remains of a group of most extraordinary 

 gigantic flightless birds which formerly inhabited that 

 country, and which are so totally 

 unlike all the modern RatitsB,that 

 there can be no reasonable doubt 

 as to their having originated 

 independently from flying forms. 

 When we have once admitted the 

 independent origin of one group 

 of giant flightless birds, there 

 appear at first sight no great 

 reasons why the modern types 

 should not have had a diverging 

 ancestry, although, as we shall 

 see later on, there are certain 

 grounds for regarding them as 

 derived from a single stock. 



For a knowledge of the giant 

 flightless birds of Patagonia we 

 are mainlyindebted to the labours 

 of Senor Florentine Ameghiuo, 

 of Buenos Ayres, from whose 

 latest work on this subject the 

 accompanying illustrations have 

 been copied. The first example 

 of their remains brought to light 

 was a portion of a lower jaw, and 

 so massive and unbird-like was 

 this bone that it was at first 

 described as belonging to a 

 gigantic edentate mammal. And 

 no wonder either, for we have 

 not hitherto been accustomed 

 to deal with birds whose lower jaw measures about twenty- 

 one inches in total length, as does the specimen represented 

 in our first illustration. Indeed, it is even now difficult 

 to convince English naturalists that the fossilized 

 extremities of the beaks of these extraordinary birds are 

 avian at all. At the end of 1893 I brought home such a 



Fio. I. — Lower Jaw of I'ho- 



rorhachis loiigisaima. • About 



one-seventh natural size. 



