Gambhir, Ring, and Schuck Respond:We agree with the author of the Comment 1 that the staggering mentioned in our Letter can be reproduced already with the use of an appropriate mass formula based on the liquid-drop model. We disagree, however, with the conclusions in the Comment as follows:(i) The liquid-drop parameters are adjusted to experimental masses and therefore do not allow any conclusions about correlations.(ii) a correlations depend certainly on the underlying basis. If one uses a Hartree-Fock-Bogoliubov basis, which takes care of the symmetry energy, one eventually does not need additional correlations. In order to show this, however, one should carry out Hartree-Fock-Bogoliubov calculations with a realistic interaction over a large number of nuclei and compare with experimental masses, a program which is probably hard to carry out. If one works with many interacting valence particles, as we do, one has to take care of the symmetry energy in the form of correlations. In our case these are four-body correlations and we call them a correlations. The importance of a correlations in this context has been stressed already in Ref. 2, where it is shown that from SU(4) symmetry one can derive the symmetry-energy term in the mass formula.(iii) It is certainly clear, and we emphasized this in our Letter, that the simple Q-Q interaction in IBM2 is probably too simple to explain the staggering quantitatively. We used this simple force only as a model in order to show that a correlations can be described in terms of bosons.

Using the Orbscan II device, the forward protrusion of the posterior corneal surface appears to coincide with a paradoxical reduction in depth of the anterior chamber. Although the keratectasia found in this study is accompanied by thin postoperative corneas and larger central pachymetry change, the contradictory decrease in anterior chamber depth creates uncertainty of measurement, and of ectasia as a mechanism of regression.

1. A complete replacement arthroplasty of the hip is described in which both components are inherently stable. 2. The arthroplasty does not require the use of acrylic cement. 3. It is appropriate for the treatment of the severely arthritic hip in which arthrodesis is not indicated, and for the mobilisation of two stiff and painful hips at any age. 4. It can be performed on both sides at the same time. 5. It produces a stable, pain-free and mobile joint in a high proportion of cases, and has appeared not to deteriorate over periods of up to four years.

This work was begun as an investigation into the characteristics of passive movement sense at the metatarso-phalangeal joint. Since the original work of Goldscheider (1889), other investigators (Winter, 1912; Laidlaw & Hamilton, 1937 a, b;Cleghorn & Darcus, 1952) have investigated joint sensation in normal subjects by measuring the response to a continuous movement. Their work established the existence of threshold speeds of movement, varyingwith different joints in different subjects, below which sensation of movement in a relaxed limb was either absent, or present irregularly and inconstantly.In the present investigation speeds were used considerably above the threshold values, but not so fast as to introduce complications resulting from variations in reaction times. The toe was displaced at a uniform angular rate and the subject responded as soon as the sensation of displacement was appreciated. The results were expressed in degrees of joint rotation, hereafter called the reaction angle. The experiment was carried out on eighty-four volunteer subjects, all medical students, in an endeavour to establish a normal range for sensation of passive movement.An initial investigation was carried out to test whether the reaction angles did in fact represent a true sensation and were not distributed at random. An analysis of variance carried out on the data left no doubt that the reaction angles represented a real measurement; some variability was shown within the scores for each foot of each subject and between the averages of the two feet of the same subject, but far greater variability was present between average scores for different individuals. Further, this initial investigation revealed no significant differences between reaction angles for the same subject at the three different speeds used (0.2, 1 and 2°/sec), although, at the slowest speed, judgement of the moment at which unequivocal sensation of movement

1. An experimental study of the effects of nerve and muscle lesions upon the growth of bone has been made. In each case animals were subjected to unilateral lesions in the hind limb, the other limb serving as a control. The growth of the tibia was measured by calculating the difference between the length of the bone on a radiograph at the beginning of the experiment and the length of the dried bone after necropsy. The weights of the dried bones were compared. 2. In the young rabbit simple exposure of the common peroneal nerve, or division of the sural nerve, produced no change in the growth rate of the tibia. Division of both peroneal nerves, producing paralysis of the muscles below the knee, led to lengthening of the affected tibia, and this lengthening persisted until maturity several months later. A similar lengthening was seen after division of the tendons around the ankle. In spite of this lengthening the tibia on the side of the operation was almost always lighter than its fellow. 3. In the puppy division of the anterior nerve roots supplying the hind limb produced a significant lengthening of the tibia of the affected limb three months after operation. No significant changes in limb length occurred after lumbar sympathectomy in the puppy. 4. The significance of these experimental nerve lesions has been considered together with recent observations upon the growth of bone in the presence of lower motor neurone lesions in the child. From this analysis it is suggested that the initial effect of paralysis is to produce lengthening of the affected bone. This lengthening is probably due to the hyperaemia of disuse. In the presence of persistent paralysis the growth of the limb is ultimately depressed. This depression is rarely seen in the experimental animal because the growing period is relatively short. The possible causes of this secondary depression of bone growth have been considered.