366 

effect of this is probably less important as the voltage 
is raised. The precision of the method would be 
enhanced if steps were taken to standardise apparatus _ 
and technique, so that all work could be done by the 
use of, say, three or four spectra the distinctive features 
of which, including energy distribution, could be deter- 
mined and specified. 
Among the other interesting aspects of the X-ray | definition. 
tube is the distribution of the rays in different direc- 
With the usual 45° target the 
rays are most intense at right angles to the cathode 
For radiographical purposes it is often 
better to mount the target face more nearly at right 
tions from the target. 
ray beam. 
NATURE 
[Marcu 17, 1923 
thick and a window of soda-glass for letting out the 
rays is to be commended on this score. Equally 
* 
robust is the new miniature dental tube of similar , 
design which measures only 4 to 5 inches long and 
has a diameter of about 13 inch. It is operated at 
45,000 volts and 1o milliampere$, is mounted in the ~ 
same oil-tank as the transformer, and gives excellent — 
protection which the radiographer has a right to demand. 
In this connexion we may confidently look forward to — 
a time at no very distant date when, in the interests 
of the operator, all protective material and apparatus 
shall be certified by the National Physical Laboratory. 
angles to the cathode beam and thus employ a pencil-| This will be realised when I mention that different 
of rays which leaves the target face at a relatively 
The width of the focal spot is thus 
small angle. 
foreshortened and definition enhanced. 
If penetrating power is the important factor, then 
we may well endeavour to utilise the X-rays leavin ng 
cl 
the tube in the direction of the cathode rays, whié 
X-rays are of appreciably shorter wave-length than in 
Thus a tube in which the he 
other directions. 
also served as a metal window would offer advantag 
on this score. 
The proper choice of filter may do much to increase 
For example, it is known, 
that, weight for weight, silver is relatively more trans- [> 
parent than lead to short w aves, but is relatively less 
Again, copper is rela- 
tively superior to aluminium in letting through short 
waves, but relatively inferior as a filter if long waves 
the effectiveness of a tube. 
transparent to longer waves. 
are required. 
What has the future in store for us as regards 
Higher voltages are coming—one hears 
rumours of 500,000 volt tubes in Germany ; and both 
the United States and Germany have, I understand, 
The 
there will 
be many difficulties to overcome before a 500,000 volt 
X-ray tubes ? 
developed transformers giving 1 million volts. 
life of 200,000 volt tubes is none too long ; 
tube will become a practical proposition. 
A crying need is more robustness in the X-ray tube, 
The 
which must become more of an engineering job. 
makes of lead-glass on the market differ by roo per 
cent. in protective value. The same remark applies 
to lead-rubber. us 
What should be our ideal in radiography ? To make 
the process as simple and noiseless as taking an ordinary 
photograph. The patient should hear nothing un- 
toward, the apparatus should look no more formidable 
than a camera. Spark and brush discharges should 
be taboo ; the rumble of rotating machinery anathema. 
Standardised technique must be the order of the day 
for much of the radiographer’s work. The number of 
variables must be cut down. 
It is possible that the future may witness the fuller 
development of the metal X-ray bulb of a design 
radically different from the present. Much work is 
being done on them at the present time. But in 
almost every section of a radiographer’s X-ray equip- 
ment there is room for great ifmprovement. How low 
the efficiency is may be gathered from the following. 
We may take it that the efficiency of the high-tension 
generator is of the order of 50 per cent., that of the 
X-ray bulb 1/1000. 
emitted by the bulb are utilised, that half these useful 
rays are arrested by the object, and that 1 per cent. 
of the remainder is recorded by the photographic 
plate or screen (rather more, say 5 per cent., if an 
intensifying screen is used). 
of an X-ray equipment is of the order of I in 
portable Coolidge tube with lead-glass walls } inch | 800,000. 

An Inquiry into Dog Distemper. 
OR some considerable time it has been felt in this 
country that an investigation might be under- 
taken with advantage on the mystery of dog distemper, 
and the matter has ‘recently been brought to a head by 
an appeal from the editor of the Field to dog lovers. 
A considerable sum of money has been promised, and 
the Medical Research Council has undertaken to 
organise an experimental inquiry with a view of finding 
out the causal agent of the disease and possibly a 
prophylactic. As announced in Nature of March 
10, a committee has been appointed under the chair- 
manship of Sir William Leishman, the other members 
being J. B. Buxton, S. R. Douglas, F. Hobday, and C. J. 
Martin. Other workers, it is suggested, will be co-opted 
for special investigations later on, 
Distemper is an acute highly contagious disease, pre- 
senting sy mptoms somewhat analogous to measles in 
man. While some have regarded it as specific for the 
NO. 2785, VOL. 111] 
dog, others consider that it occurs in cats, young foxes, 
wolves, jackals, hyzenas, and even monkeys. From its 
contagiosity it is certain that the cause is a microbe of 
some kind, which, however, has hitherto remained un- 
masked. 
knowledge extant on the disease. This is in part, at 
any rate, due to the fact that what veterinary surgeons 
and the laity call distemper is almost certainly not one 
but several different diseases. That one of these is the 
specific disease distemper is, however, very probable. 
At present the concept of “ distemper ” is entirely 
clinical. 
of catarrhal, gastric, nervous, and exanthematic types 
of the disease. 
show that one attack of the malady confers a durable 
immunity on the survivor. The disease occurs in all 
countries and was apparently known in antiquity. On 
the other hand, there is a tradition—it is little more— 
It also contributes substantially to the 
We may assume that half the rays 
Thus the overall efficiency 
Indeed, there is very little real scientific — 
Thus, one finds descriptions in the literature — 
There is a great body of evidence to — 

: 
