568 



NATURE 



[April i6, 1896 



and has been developed to a stage in which, failing the latter 

 contingency, it is likely to be widely accepted. Assuming it 

 to be correct, man occupies to the parasite the position of what 

 he terms an '_' optional host," in which parasitism is neither 

 necessary for nor inimical to the continuance of the species. 



Another case of such possible relationship may be mentioned. 

 In 1889, it was shown by Drs. Smith and Kilborne ^ that the so- 

 called " Red-water " or " Texas fever" of cattle is a disease of 

 malarial type due to the presence in the red blood-corpuscles of 

 bodies presenting a certain similarity to Laveran's parasite. In this 

 disease the sole form of infection known is by the agency of 

 cattle-ticks (I.xodidae), in which, notwithstanding their un- 

 doubted transmissive part, we believe the entozoon has hitherto 

 not been detected in any stage. 



Without attempting in any way to prescribe a line of research 

 which Dr. Bruce is unlikely to overlook, it is impossible not to 

 foreshadow the interest which will attach to an examination of 

 the evolutions of the parasite in the body of the Tsetse, an 

 examination which may end by showing that the insect, even if 

 it possesses no specific virus in the older sense, may play an 

 essential part in the economy of the htematozoon. 



The symptoms, course, and pathology of Nagana are treated 

 very fully by Dr. Bruce in a series of clinical cases, accompanied 

 by charts indicating the variations of temperature, and the per- 

 centages of red blood-corpuscles and ha;matozoa. Suffice it 

 here to say that the red blood-corpuscles may be reduced to one- 

 third of their normal amount, and in one dog, at the point of 

 death, bore to the parasites the proportion only of ten to one. 

 He finds it invariably fatal in the horse, ass and dog'— perhaps 

 not necessarily so in cattle — in which it runs a much slower 

 course. Two graphic and painful pictures are given of a donkey 

 and a dog in the last stage of this distressing disease, and one 

 is glad to learn that there is little suffering, and that the appetite 

 rarely fails up to the last. 



Of the new facts contained in this report, perhaps the most 

 welcome is that Dr. Bruce finds that arsenic, so far as he has 

 been able to try it, has a marked action on Nagana, causing 

 disappearance of the hrematozoa, reduction in temperature, and 

 maintenance of the normal number of red blood-corpuscles. 

 That it is a complete cure or prophylactic remains to be shown. 

 The same result has been found in Surra, though the proportion 

 of cases mentioned by Dr. Lingard as cured by treatment with 

 arsenic is but small. This appears to be due partly to the extreme 

 debility of many animals at the time of its first administration, 

 and to the large and sometimes poisonous doses required. Its 

 effects, nevertheless, are so remarkable as to give good ground 

 for hoping that, when the limits of utility and safety of the drug, 

 especially as a preventive, or in the early stages of disease, are 

 determined, the trivial addition of a supply of arsenic to the 

 traveller's outfit will free the African colonist of, perhaps, his 

 greatest source of anxiety. 



In Surra attempts have been made to treat the disease 

 by inoculation or injection of filtered serum from affected 

 animals. They have not proved successful, nor, while admitting 

 the importance of the fact that the range of forms attacked by it 

 and Nagana is limited, is there any a priori reason why they 

 should succeed. The class of diseases here noticed, of which 

 malaria may be taken as the type, is not caused by bacteria ; 

 and though it is known that the vitality of hajmatozoa is affected 

 by alterations in the medium in which they live, as by the 

 administration of quinine or arsenic, the ordinary methods of 

 research and antitoxic treatment employed in bacteriology do 

 not appear to be applicable to them. 



In view of a tendency in the reports, both of Dr. Bruce and 

 Dr. Lingard, to dwell in detail upon the clinical features of the 

 respective diseases, it cannot be too strongly urged that, when 

 once the pathogenic nature of the hsematozoon has been estab- 

 lished, these inquiries, in order to progress to a fruitful issue, 

 inust be conducted on zoological lines. The mode of reproduc- 

 tion, distribution and general bionomics of the hrematozoon, 

 and, in the event of its possessing more than an accidental 

 connection with the Tsetse, the economy of that insect, these 

 are the essential subjects of research : and little light will be 

 thrown on them by any amount of laboriously-compiled clinical 

 and pathological details. 



It is to be desired that Surgeon-Major Bruce's further and 

 more complete reports shall be republished in England, or at 

 least made easily accessible to the many persons interested in 

 African colonisation. Walter F. H. Blandford. 



Ann. Rep. U.S. Sec. 

 ; and following year. 



Agrk. 



92, 93, and 105- 



THE ACTION OF LIGHT ON THE IRIS,. 

 DEMONSTRATED BY A NEW PUP HO- 

 ME TER. 



"DROWN-S^QUARD observed that, in the iris of batrachians. 

 and fishes, separated from the rest of the eye, the pupil 

 contracts at the approach of a candle, a fact which he attributed 

 to the direct action of the light on the muscular tissues of the 

 iris, the nervous elements having already lost, as he thought, at 

 the times of his experiment, all irritability. We may also ask 

 if the iris of the living eye responds to the direct action of 

 light. 



This problem cannot be approached directly, because of the 

 mobility of the eye and the extreme variability of the pupil. 



My new pupilometer, constructed by the well-known engineer, 

 Mr. Ph. Pellin, consists of a series of three tubes of increasing 

 diameter, commencing with the ocular tube ; the first is pro- 

 vided with a screen perforated by a very small hole, and with 

 an adjustable frame which may be removed or brought near in a 

 manner to fix the eye at the required distance {i2-8 mm.), 

 of the anterior focus of the eye. The last tube is closed 

 by a ground glass, lo cm. in diameter ; on the surface of 

 this glass appear black and white circles with numerical 

 graduations. All the peripheric zones of the ground glass which 

 are not perceived by the retina illuminate the iris. In this manner 

 I am able to distinguish the effect produced upon the pupil by 

 suppressing the illumination of a portion of the iris by means of 

 opaque rings of blackened copper successively arranged upon the 

 glass, the apertures of which are precisely equal to the apparent 

 surfaces of the pupil, and then suddenly removed. For the 

 retina nothing is changed by changing these rings, since the 

 opening of each ring equals precisely the apparent surface of 

 the luminous admission ; for the iris, on the contrary, all is 

 changed, since the opacity of the interposed rings prevents the 

 luminous rays from reaching it. 



The experiment made under these conditions proves that there 

 is almost always a dilatation of the pupil when the iris is with- 

 drawn from the light. The process may be described as follows. 

 The subject is requested to indicate the largest concentric circle 

 that he is able to distinguish on the luminous background, where- 

 upon I place against the background an opaque ring, the open- 

 ing of which equals precisely the said concentric circle ; after a few 

 moments I remove the ring, and then the subject generally re- 

 marks the coincidence of the apparent surface of his pupil with a 

 concentric circle of much greater diameter. I have noticed but 

 two exceptions to this rule where the result was a contraction 

 instead of enlargement. The dilatation varies from | to J-^ of 

 I mmq. for I mmq. of iris withdrawn from the light, and such 

 dilatation has generally been observed to be greater for the 

 dark than for the light iris. 



The great majority of dark eyes which prevails in southern 

 latitudes is perhaps a provision of nature to thus protect 

 the eye from the effect of too abrupt changes of luminous 

 irritation. 



In any case the variations of dimensions of the iris are much 

 less when it is the iris alone which is subjected to light than 

 when the iris and the retina are influenced together. It may be 

 shown, for instance, that if i mmq. of the centre of the retina be 

 withdrawn from the light, the iris is capable of increasing in size 

 from I to 16 mmq. 



If, with the pupilometer of Robert Houdin, we observe the 

 pupil of one eye while the iris of the other is obscured, we remark 

 on the said pupil a dilatation from half to quarter of a millimetre 

 in diameter ; this goes to prove that the action of light on the 

 iris is due, in part at least, to a reflex of cerebral origin ; but, on 

 the other hand, we do not yet possess sufficient knowledge of the 

 anatomy of the iris to enable us to say whether these variations 

 are due to the direct action of light on muscular elements 

 (as supposed by Brown-Sequard) or to the action of nervous 

 centres yet unknown belonging to the iris. 



I have studied the influence of a coloured disc on the pupil, 

 allowing the coloured light to strike the retina, in which cases 

 I remarked that the more luminous the colours the less the 

 dilatation of the pupil : yellow and green, for instance, cause a 

 greater dilatation than red or blue. Again, I have remarked just 

 the contrary. The same contradictions, which may be explained 

 by the fatigue of the eye, are manifest when we examine the 

 isolated action upon the iris of rings cut from the same block as 

 the aforesaid coloured disc. 



I have also endeavoured to find with the new pupilometer the 



NO. 1381, VOL. 53] 



