490 
NATURE 
[FEBRUARY 22, 1917 
over, acquainted with the morphology and some of the 
cultural characteristics of this organism, which is a 
frequent source of contamination in my laboratory. 
Further, a number of similar bacilli were found in 
the smears from the other deposits, but in every case 
they were dead and quite incapable of growth. In 
many of these smears circular bodies were also visible, 
often very suggestive of torula. They varied so much 
in shape and size, ‘however, that though some speci- 
mens were indistinguishable from living organisms, 
others were clearly irregular plates of silica which 
were capable of absorbing the usual stains. 
As a result of these experiments I am forced to 
conclude that the remarkably lifelike bodies described 
and photographed by Dr. Bastian are due to the de- 
position of silica round minute nuclei or on the detritus 
of dead organisms, in the manner described by Moore 
and by Paine,* 
I am quite at a loss to discover an explanation of 
the results of A. and A. Mary,*® whose original paper 
I have been unable to read, unless they are due to 
lack of sufficiently stringent precautions, as in the 
case of the contamination mentioned above; for when 
the greatest care is exercised, tubes prepared in this 
manner will still be absolutely sterile even after an 
interval of three years. H. Onstow. 
Biochemical Laboratory, Cambridge. 
Stability in Flight. 
ALTHOUGH I am quite incompetent to hold any 
opinion on problems in human aeronautics, I venture 
to submit that the inference drawn by Prof, D’Arcy 
Thompson from the flight of certain birds (p. 409) 
does not agree with accurate observation, and may 
prove misleading, 
Prof. Thompson’s proposition is that long’ tails 
are disadvantageous to safety and stability in windy 
weather, and that birds of skilful or agile flight are 
equipped, *‘on the whole, with small tails and compara- 
tively small and narrow wings.”’ No such generalisa- 
tion can stand in the face of facts. One has but to 
watch the evolutions of flocks of two of the commonest 
British birds—the rook with a long and broad tail, 
the lapwing with a shorter one, and both with remark- 
ably broad, rounded wings—to admire their perfect 
mastery of flight in stormy weather. 
Prof. Thompson describes the pigeon (species or 
variety not defined) as ‘‘a splendid flyer for mere dis- 
tance,’’ but indifferent in manceuvring because of its 
“large, rounded wings.’’ No species of pigeon known 
to me has rounded wings; all have them long and 
pointed, and as for “sudden and acute changes of 
course,” the pigeons in St. Paul’s Churchyard have 
inherited a remarkable faculty in that respect from 
their ‘‘ blue rock” ancestors, which had to thread their 
way at top speed through narrow sea-caves. Moreover, 
one variety—the tumblers—are perpetually ‘looping 
the loop,” notwithstanding their long tails. 
Coming to birds of prey, Prof. Thompson classes 
the kestrel with the buzzard as a broad-winged hawk, 
and remarks that falconers despised both. But the 
kestrel is a true falcon as testified by the dark iris, tne 
notched maxilla, and the long and pointed wing (the 
second and third primaries being the longest). It is 
true that falconers had little use for the kestrel, not 
because of its inferior wingmanship, for it has few 
rivals in power and dexterity of flight, but because it 
preys chiefly on mice, beetles, and other diminutive 
ground game. But the goshawk and the sparrow- 
hawk are Accipitrinze, with broad, rounded wings, the 
fourth and fifth primaries being the longest. Fal- 
4 Annals of Botany, v cx., N cix 
5 Le Médecin CBrnsealel Ocean ees Jeg bel a 
NO. 2469, VoL. 98] 
coners greatly prized the goshawk for its prowess in 
flight, and the sparrow-hawk is distinguished by ex- 
traordinary agility and quickness in turning when in 
pursuit. Two opposite types of bird may be noted as 
having long tails and superb powers of flight, viz. _ 
the kite and the nightjar, the latter taking all its prey 
on the wing. ; 
Lastly, when Prof. Thompson suggests that the 
outstretched legs of a heron act ‘‘as a very useful 
counterpoise to the long neck and bill,’’ he seems to 
have forgotten that this bird does not fly with out- 
stretched neck like a swan or a mallard. The heron 
extends its neck in rising from the ground; but so 
soon as it is fairly on the wing it tucks back its 
neck and rests its head between its shoulders, thereby 
reducing to a minimum the lengthened axis which 
Prof. Thompson regards as ‘‘contributing very 
materially to the creature’s longitudinal stability.” 
Monreith. HERBERT MAXWELL. 
I wit give in to Sir Herbert Maxwell so far as to 
say that some of my examples might have been better 
chosen; I will go further and admit that my 
kestrel was clearly not a case in point, On the other 
hand, Sir Herbert, throws more responsibility on me 
than I ever undertook, and he sweeps aside all the 
qualifying and questioning words with which I was 
careful to safeguard my letter; not that I wanted to 
hedge or hide behind these, but simply that my object 
was to suggest an inquiry, not to lay down the law. As 
to the mechanical advantages of short tails compared, 
caeteris paribus, with long tails, I made no assertion 
and laid down no proposition; but certain learned 
mathematicians had done so, bringing forward their 
proofs, and the naturalist has no right to dispute such 
abstract and theoretical demonstrations. When Galileo 
showed the mechanical advantages of a hollow pillar 
he adduced the straw and the quill as exemplifications 
of the principle; and the mere fact that so many trees 
and so many feathers are not hollow at all gives the 
naturalist no sufficient right to question it. I directed _ 
attention to the fact that Prof. Bryan and Dr. Brodet- 
sky, after demonstrating a principle, had stopped 
short of inquiring whether it could be illustrated 
by, or recognised in, the case of the living 
flying organism; I considered that there were many 
cases in which it could be so recognised, and ~ 
I am of that opinion still. We must not forget — 
that “ caeteris paribus” is an essential condition of our 
comparison, and that this condition we can only seldom 
and approximately fulfil. Moreover, we are dealing 
only with differences of degree, with grades of excel- 
lence. No one doubts that the rook flies extremely 
well, and for that matter every flying bird is mar- — 
vellous in our eyes; but for all Sir Herbert may 
say to it, I don’t believe that a flight of rooks can 
‘approach a flock of sandpipers, in the particular quali- 
ties of grace, dexterity, and precision of movement. 
As to the heron and its long neck, it would almost 
seem to me as though Sir Herbert had gone out of his 
way for the sake of fault-finding. I never said the 
heron flew with its neck stretched out; I said it flew 
with its legs stretched out. Why, I was brought up in 
my boyhood within a couple of miles of a heronry, 
and saw the birds every day of my life! But the heron 
has a long head and a long neck, and they have to be 
carried somehow; and it is somehow by help of the 
long legs that they haye to be counterpoised and 
balanced. The slender bill, narrow body, and long, 
thin legs make up a sort of long, narrow, axial frame- 
work associated with the machinery of flight. I was 
surely entitled to suggest, or to surmise, that this 
extended axis (a little like a witch’s broomstick) might 
have a notable influence on the motions of the bird, 
