AUGUST 12, 1915] 
present paper is of equal value to its predecessors. 
Milton had not the knowledge of plants possessed by 
the other three poets, but the Canon’s notes are full 
of interest. Milton’s amaranth still remains a 
puzzle, but as he places it in Paradise, further earthly 
research seems useless. 
In the current number (vol. xiii., No. 2) of the 
Imperial Institute Bulletin, Prof. J. B. Harrison 
and Mr. C. K. Bancroft contribute a paper on ‘‘’The 
Field and Forest: Resources of British Guiana.” 
Some 55,770,000 acres of land are estimated to be 
open for beneficial occupation, some 9,000,000 of 
which are easily accessible. Rice is a product which 
may be grown over large areas, and the success 
which has attended its culture shows that the colony 
might well become the granary of the West Indies 
in this particular grain. Forestry development is 
limited by difficulties of transportation, but of timber 
there is abundance and of good quality. Balata, 
which occurs all over the colony, is one of the most 
important forest trees, and greenheart is perhaps the 
best known of all the timbers of British Guiana. 
At the monthly general meeting of the Zoological 
Society of London, held July 21, special attention 
was directed to the hatching, in the menagerie, of 
a white-browed wood swallow and two white storks. 
Since the total number of visitors to the Gardens 
between January 1 and June 30 shows a decrease of 
120,993, it would seem that the war has, during this 
period, seriously crippled the Society; but matters 
are, happily, not so bad as this statement, in itself, 
would seem to show, for the receipts for admission 
at the gates, as compared with the corresponding 
period for the last ten years, show a deficiency of no 
more than 4o4l., which may well be made up during 
the next few months. 
THE investigation of another egg of Ornitho- 
rhynchus, described in the current number of the 
Quarterly Journal of Microscopical Science (vol. 1xi., 
part i.), has afforded Rrofs. Wilson and Hill an 
opportunity of revising their views on the subject of 
the so-called primitive or archenteric knot. This 
structure was supposed to mark the position of the 
blastopore, but to come into relation with the primi- 
‘tive streak only secondarily, originally lying outside 
the embryonic shield. Both Keibel and Assheton 
criticised this interpretation, and suggested that the 
supposed archenteric knot in the younger stages of 
Ornithorhynchus might in reality be the yolk-navel. 
This view is definitely accepted by Profs. Wilson and 
Hill, who state that they feel with Assheton that 
“another stumbling-block has been removed from 
the path of the student of mammalian embryology.”’ 
THE way in which animals learn by the method of 
so-called trial and error has now been rendered fairly 
comprehensible by a considerable body of experimental 
work, largely conducted in the psychological labora- 
tories of the United States. In a recent ‘‘ Behavior 
Monograph”’ (No. 10) of the well-known series edited 
by Prof. J. B. Watson, Mr. J. L. Ulrich discusses 
the distribution of effort in learning in the white 
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NATURE 

653 
rat. The chief questions to which he seeks an 
answer are these: Given three ‘‘problems ”’ to be 
practically solved by behaviour which has to be learnt, 
what in each several case is the optimum distribu- 
tion of trials; once in three days, once a day, or thrice 
a day? The answer seems to be that once in three 
days gives the minimum number of trials before the 
lesson is completely learnt, but that with three trials 
a day the lesson is learnt in a shorter period of time. 
It seems, too, that when three modes of behaviour are 
learned abreast, trials in each being made on the 
same day, infrequent practice, say one trial in each 
per diem, is advantageous, and that under these con- 
ditions a much larger number of trials is required 
for the solution of each of the problems than is 
required when the modes of behaviour are learnt one 
at a time. Physiological interpretation is tentatively 
suggested. 
In a series of three papers published by the Edin- 
burgh and East of Scotland College of Agriculture, 
Dr. J. P. M’Gowan discusses the epidemiology and 
pathology of three important animal diseases, swine- 
fever, louping-ill of sheep, and  chicken-cholera. 
Louping-ill he considers to be caused by the Bacillus 
bipolaris septicus ovium; the disease is divisible into 
several varieties, and a “pseudo-louping-ill”’ is also 
known. Swine-fever is generally considered to be 
caused by a ‘“‘filter-passer,” but the view is expressed 
that the evidence for this being the case is far from 
complete. Chicken-cholera is caused by the Bacillus 
pullorum, but there are probably several varieties of 
this organism, and ‘‘white diarrhcea” of poultry and 
“white scour” of lambs are probably caused by 
similar micro-organisms. 
In an article on the production of X-ray bulbs in 
France (La Nature, July 10) it is pointed out that the 
statement that suitable French glass was not avail- 
able at the outbreak of war was inaccurate. Since 
1904 Appert Bros. have made suitable glass, and that 
though glass blowers preferred Thuringen glass, it was 
on grounds of economy only, and the Clichy factory 
was able to supply similar glass when the stocks 
became exhausted. From analyses of German glass 
by M. Matignon it was found possible to imitate it, 
and glass even more transparent to X-rays is now 
made. Pilon’s modification of the Coolidge tube is 
described, showing how satisfactory cooling of the 
antikathode is obtained. The 1915 model gives a 
steady discharge even for such long periods as 1 hour 
20 minutes, with perfect control of the character of 
discharge. 
La Nature for July 10 also contains a very interest- 
ing article on the torpedo. Reference is made to the 
early history of the torpedo; to Whitehead’s early 
pattern of a speed of only 6 knots, and capable of 
covering a distance of 600 metres. The great pro- 
gress made to the present torpedo, with a speed of 
45 knots and 10,000 metres range, carrying a charge 
of 150 kilos. of high explosive, is a notable achieve- 
ment. An excellent description is given of the manner 
in which the difficulties of control] of immersion and 
direction have been overcome by means of the hydro- 
